Does Bilingual Early Education Delay Speech? What the Research Says
A factual look at the science behind bilingual language development in young children, addressing common concerns about speech delay and language mixing.
One of the most common questions parents ask before enrolling a child in a bilingual nursery is whether learning two languages at once will slow down their speech development. It is a reasonable concern — but the scientific evidence is reassuring, and a few persistent myths are worth addressing directly.
The short answer
Bilingual children are not delayed in language development compared to monolingual children when measured fairly. The key phrase is measured fairly — and that is where much of the confusion originates.
Where the concern comes from
Early studies comparing bilingual and monolingual children sometimes showed smaller vocabularies in each individual language among bilingual children. This was interpreted by some as evidence of delay. The problem was the measurement: if you test a bilingual child only in English and count only English words, you will get a smaller number than a monolingual child of the same age, because the bilingual child's vocabulary is spread across two languages.
When researchers measure total vocabulary across both languages — the correct method — bilingual children score comparably to monolingual peers. Studies by researcher Ellen Bialystok at York University, who has spent over four decades researching bilingualism, consistently show that bilingual children reach the same developmental milestones as monolingual children when assessed across both languages.
What bilingual children sometimes do differently
Language mixing — switching between languages within a sentence or conversation — is normal in young bilingual children and is not a sign of confusion or delay. It reflects the child drawing on both language systems as they develop fluency. Most children naturally code-switch less as they grow older and become more aware of which language is expected in which context.
A slightly smaller vocabulary in each individual language is typical for bilingual children, but this reduces and largely disappears as children progress through primary school, and it is not the same as a language disorder or delay.
A brief settling-in period is common when a child joins a nursery in a new language. This is a normal phase of language acquisition, not an indicator of a problem with the child's development.
What the research is clear on
A substantial body of research — including work by Dr Patricia Kuhl at the University of Washington and Laura-Ann Petitto at Gallaudet University — supports the following conclusions:
There is no critical developmental harm from bilingual exposure in infancy or early childhood. The brain is not confused by two languages — quite the opposite. Research suggests that managing two language systems may strengthen certain executive function skills, including attention and cognitive flexibility.
Early childhood is the optimal window for acquiring a second language with native-like fluency. The neural plasticity that makes early language acquisition so efficient begins to reduce from around seven years old. A child who acquires a second language before the age of five is more likely to develop native-level pronunciation and grammatical intuition than a child who begins later.
Children do not become permanently confused about which language is "theirs". Even very young children show an awareness of when to use which language, switching naturally depending on who they are speaking to.
When to seek advice
Bilingual education does not cause language disorders or speech and language delays. However, if you have concerns about your child's language development — in either language — it is always worth raising with your health visitor or GP, or requesting a referral to a speech and language therapist.
A speech and language therapist assessing a bilingual child should evaluate development across both languages. Assessment in only one language risks both over- and under-identifying difficulties.
Signs worth discussing with a professional regardless of bilingual status include: not babbling by 12 months, no single words by 16 months, no two-word phrases by 24 months, or loss of previously acquired language skills at any age.
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