A parent hears their three-year-old speaking in short, mixed-up sentences — a little English, a little Spanish, a word order that belongs to neither — and starts to wonder whether two languages were a mistake.
Then a relative says something confident: that's why he's behind. Pick one.
It is one of the most persistent myths in child development, and it reliably produces one of two bad outcomes. Some families drop a language they did not want to drop. Others wait a year on the assumption that bilingualism explains everything, when something else was going on the whole time.
The research here is clearer than most questions in our field. Let's go through it.
The Short Answer
No. Being bilingual does not cause a speech or language delay.
ASHA's practice portal on bilingual service delivery puts it in one sentence: "Being multilingual is not a communication disorder, but it is a significant consideration when there are concerns regarding a hearing or communication disorder."
Both halves of that sentence matter. Bilingualism is not a cause. But it does change what typical development looks like, and it changes how an evaluation has to be done — which is precisely why bilingual children get misjudged in both directions.
For context, this is not an edge case: ASHA notes that 22% of the U.S. population speaks a language other than English at home.
What the Research Actually Shows
Milestones arrive on schedule
The strongest evidence against the "two languages confuse them" idea comes from studying children who had two languages from birth. Petitto and colleagues (2001) followed children acquiring two languages simultaneously — including one group acquiring a signed and a spoken language, which lets you see the two systems separately. Both groups "achieved their early linguistic milestones in each of their languages at the same time (and similarly to monolinguals)."
The children also produced translation equivalents — words for the same concept in both languages — from their very first words, and adjusted which language they used based on who they were talking to. The authors concluded that "the capacity to differentiate between two languages is well in place prior to first words."
Children are not confused about which language is which. They sort that out before they can say anything at all.
Vocabulary is distributed, not diminished
This is where almost all the misreading happens. Hoff and colleagues (2012) compared bilingual and monolingual children from roughly 22 to 30 months. The monolingual children were significantly ahead on vocabulary and grammar — when measured in one language at a time. But the groups were "comparable on a measure of total vocabulary."
The follow-up study by Core, Hoff, Rumiche, and Señor (2013) looked specifically at what this means for screening. Across 47 Spanish-English bilingual children and 56 monolingual controls, total vocabulary — everything the child knows in both languages combined — produced mean scores and growth rates similar to monolingual growth. Critically: "Total vocabulary identified the same proportion of bilingual children below the 25th percentile on monolingual norms as the CDI did for monolingual children."
Translated: if you count both languages, a typical bilingual toddler looks typical. If you count one, a meaningful number of perfectly fine children look delayed.
The same study found that conceptual vocabulary — counting a concept once even if the child has the word in both languages — came out significantly smaller and grew more slowly. Which measure you pick changes the answer. That is a measurement artifact, not a child problem.
Hoff's study also found something practical: within the bilingual group, every vocabulary and grammar measure tracked the relative amount of input in that language. Children know more of the language they hear more. That is not a disorder; it is arithmetic.
Speech sounds: small differences, different kind
For pronunciation specifically, the most comprehensive look is a systematic review by Hambly, Wren, McLeod, and Roulstone (2013), covering 66 studies — 53 of typically developing bilingual children and 13 of bilingual children with speech sound disorder.
Their finding: "There was limited evidence to suggest that bilingual children develop speech at a slower rate than their monolingual peers; however, there was evidence for qualitative differences and increased variation in speech production."
So bilingual children are not slower to acquire speech sounds in any well-supported way, but their error patterns can look different, because features transfer between the two sound systems in both directions. Positive transfer became more evident with age and length of exposure.
The review opens with the clinical problem that motivated it, and it is worth quoting as a warning: children who are bilingual and have a speech sound disorder "are likely to be under-referred, possibly due to confusion about typical speech acquisition in bilingual children."
That is the real risk in this topic. Not over-diagnosis. Under-referral, because bilingualism was offered as the explanation and nobody looked further.
Four Things That Are Normal and Get Mistaken for a Delay
Language mixing. Using two languages in one sentence is skilled behavior, not breakdown. ASHA describes code-switching as possibly "a cognitive strategy for multilingual people to easily access all the languages they know in order to provide alternate ways to convey meaning." Petitto's study added a useful detail: how much children mixed was directly related to their own parents' mixing rates. They are copying the conversational norm in front of them.
A smaller vocabulary in each language separately. Covered above. Count both.
A silent period. This one applies to children who meet a second language later, typically after age 3 — what ASHA calls sequential acquisition, as opposed to simultaneous acquisition where all languages arrive before age 3. ASHA notes that "a silent period may occur during the initial phase of second-language acquisition while an individual focuses on listening and comprehending the new language," during which the learner can understand far more than they can produce. A quiet first few months in a new preschool is often this, not a regression.
A long, uneven runway to English. Paradis (2016), reviewing research on English language learners, found that they "take longer than 3 years to converge on monolingual norms and approach monolingual norms asynchronously across linguistic subdomains." Vocabulary, grammar, and narrative skills do not arrive together. A child can sound conversationally fluent and still be behind on the grammar a test measures.
The One Signal That Matters: Both Languages
Here is the principle that does most of the work:
A genuine speech or language disorder shows up in both languages. A child who is behind only in the language they hear less often is showing an exposure difference. A child who is behind in both is showing something that belongs to the child, not to the language environment.
Concretely, these are worth an evaluation:
- Limited vocabulary in both languages, counted together
- Short, ungrammatical sentences in both languages, well past the age peers are combining words
- A history of late babbling and late first words in the home language, before English was ever in the picture
- Speech that unfamiliar listeners cannot understand in either language
- Difficulty following directions or understanding questions in the language the child hears most
Paradis's review found that children learning English as a second language who also had a language disorder acquired English more slowly than their typically developing peers, and that "their morphological and nonword repetition abilities differentiate them the most" — grammar details and the ability to repeat made-up words, both of which depend less on how much vocabulary a child happens to have been exposed to.
If the concerns are the same in both languages, bilingualism is not the explanation, and waiting on that assumption costs time. Our guides to speech milestones by age and signs your child needs speech therapy are the right next read, with the "in both languages" filter applied to everything on them.
Should We Drop a Language?
No — and this comes up most often after a child receives a diagnosis, when a well-meaning professional suggests simplifying to English.
The best available synthesis is a practitioner review by Uljarević, Katsos, Hudry, and Gibson (2016), covering 50 studies of multilingualism in children with neurodevelopmental disorders — 38 in communication disorders, 10 in autism, 2 in intellectual disability. When multilingual children with a disorder were compared with monolingual children with a similar disorder, "the findings consistently show no adverse effects on language development or other aspects of functioning." In autism specifically, a positive effect on communication and social functioning has been observed.
Their conclusion: "There is little evidence to support the widely held view that multilingual exposure is detrimental to the linguistic or social development of individuals with neurodevelopmental disorders." The authors are honest about the limits — the pool of studies is small and relatively few are methodologically strong. But the direction of the evidence does not support dropping a language, and the burden of proof sits with the advice to drop one.
The costs on the other side are concrete. A child who loses the home language loses conversation with grandparents, and parents end up supporting their child in a language they themselves are less fluent in. Paradis and colleagues (2010) observed first-language loss in both typically developing children and children with language impairment in their sample — it happens quietly once school-language exposure dominates.
ASHA's own position asks clinicians to "advocate for the benefits of multilingualism to families who may have been told — or made to feel — that they should avoid using certain languages with their children and family members." If you have been made to feel that way, that is the professional consensus disagreeing.
How a Bilingual Child Should Be Evaluated
A few things separate a good bilingual evaluation from a bad one:
Both languages get sampled. ASHA's standard is that the clinician obtains single-word and connected-speech samples "in all languages used by the client — through collaboration with an interpreter, if necessary." A test administered only in English measures English exposure as much as it measures ability.
Scoring accounts for two languages. Total vocabulary rather than single-language counts, per Core et al. Standardized tests normed on monolingual children are used carefully or not at all.
Parent report on the home language counts as data. Paradis and colleagues developed a parent questionnaire (the ALDeQ) for exactly the common situation where the first language cannot be assessed directly — with 139 typically developing children and 29 with language impairment, it discriminated meaningfully between the groups, and the early-milestones section was the strongest single discriminator. Notably, it had better specificity than sensitivity, meaning it is better at confirming typical development than at catching impairment — a tool to use alongside others, not alone. If you are a parent, your account of when your child babbled, said first words, and started combining them in the home language is genuinely diagnostic information.
Hearing is checked. Always, and first.
Where We Fit — Said Plainly
Bloom provides evaluation and therapy in English. Laura Friedman is a certified speech-language pathologist (CCC-SLP) and Qualified Orofacial Myologist, not a bilingual service provider, and we are not going to pretend otherwise on a page about this topic.
What that means in practice:
- If your child's stronger language is not English, ASHA's standard calls for assessment in all the languages they use. That requires a bilingual SLP in that language or a trained interpreter. We will tell you that rather than run an English-only evaluation and hand you a number that does not mean what it appears to mean.
- If your child is bilingual and English-dominant — common for children born here to multilingual families — we can evaluate and treat in English, with your report on the home language built into the history.
- Some concerns are the same in every language. A tongue thrust, a tongue-tie, an orofacial myofunctional disorder, or a feeding difficulty is a structural or habit-based issue, not a linguistic one. Tongue thrust distorts /s/ and /z/ in whatever language a person is speaking. These do not require a bilingual clinician to identify or treat.
If you are weighing whether what you are seeing is bilingual development or something that needs attention, the most useful thing we can do is help you tell the difference — including telling you that your child looks fine, or that the right next call is to someone else.
Frequently Asked Questions
Does being bilingual cause a speech delay?
No. ASHA states plainly that "being multilingual is not a communication disorder." Children acquiring two languages from birth reach their early linguistic milestones in each language on the same schedule as monolingual children (Petitto et al., 2001). What bilingualism changes is how vocabulary is spread across two languages — which is why a single-language test can make a typically developing bilingual child look behind.
Why does my bilingual child seem to know fewer words than other kids?
Because the count is usually being taken in one language. Hoff et al. (2012) found monolingual toddlers ahead on single-language measures but "comparable on a measure of total vocabulary." Core et al. (2013) found that total vocabulary flagged the same proportion of bilingual children below the 25th percentile as the standard measure did for monolingual children. Count both languages first.
Is it normal for my child to mix two languages in one sentence?
Yes. ASHA describes code-switching as possibly "a cognitive strategy for multilingual people to easily access all the languages they know." Petitto et al. also found children's mixing rates tracked their parents' mixing rates — it is a learned conversational pattern, not confusion.
How do I know if my bilingual child actually has a delay?
A real disorder shows up in both languages. Behind only in the less-used language is an exposure difference. Limited vocabulary in both, short ungrammatical sentences in both, or a history of late babbling and late first words in the home language — those warrant an evaluation, and bilingualism is not the explanation for them.
Should we stop speaking our home language?
No. A review of 50 studies on multilingualism in neurodevelopmental disorders found "no adverse effects on language development or other aspects of functioning" when multilingual children with a disorder were compared to monolingual children with a similar disorder, with a positive effect observed in autism (Uljarević et al., 2016). ASHA asks clinicians to advocate for the benefits of multilingualism. Dropping the home language has real family costs and no demonstrated benefit.
My child went quiet after starting an English-speaking preschool. Is that bad?
Often it is a silent period — a documented phase in second-language acquisition where the child focuses on listening and comprehending, understanding much more than they produce. ASHA describes it as part of the initial phase of learning a second language. If it persists for many months, or if the home language also regresses, have it looked at.
Can Bloom evaluate a bilingual child?
We provide services in English. For a child whose stronger language is not English, ASHA's standard calls for speech samples in all languages the child uses, which means a bilingual SLP or a trained interpreter — we will say so rather than evaluate around it. For English-dominant bilingual children, and for concerns that present identically in any language (tongue thrust, tongue-tie, orofacial myofunctional disorders, feeding), we can help directly.
Not Sure Whether to Wait or Get It Checked?
If your child is growing up with two languages and you have been told to wait because that explains it, the question worth answering is narrower than it sounds: is the concern present in both languages? That one distinction separates normal bilingual development from a delay that deserves attention.
Schedule a free consultation with Laura Friedman, CCC-SLP — in person in Dallas or by telehealth nationwide. We will walk through what you are seeing in each language, what your child's early history in the home language looked like, and whether this needs a speech and language evaluation, a referral to a bilingual provider, or nothing at all. Our pages on language delays and speech therapy for children cover what treatment looks like if it turns out to be warranted, and is speech therapy effective for toddlers? covers what the evidence says about acting early.