One of the most persistent myths in parenting culture is that raising a child in two or more languages delays their speech. The myth survives despite decades of research consistently showing it's wrong. This guide walks through what the bilingual-development research has actually found — including the small kernel of truth that gives the myth its surface plausibility.
The Short Answer
Bilingual children hit the same language milestones as monolingual children — when you count their total vocabulary across both languages. The myth comes from looking at only one language at a time. A bilingual 18-month-old may have 25 English words and 25 Spanish words; counting only the English makes them look like a late talker.
Pediatric speech-language pathologists routinely use total conceptual vocabulary (every distinct concept the child has a word for, in either language) as the appropriate metric for bilingual children. By that measure, bilingual children are on par with monolingual peers throughout early childhood.
Where the Myth Comes From
Three things have contributed to the persistence of the myth:
- •Older research design problems. Some early bilingual-language studies measured only one language and found bilingual children behind — but the methodology was flawed.
- •Per-language vocabulary often is smaller. A bilingual 24-month-old may have 80 words in Spanish and 80 in English, vs. 150+ for a monolingual peer. The total (160) is comparable; the per-language number isn't. Pediatricians not trained in bilingual development sometimes still apply monolingual norms.
- •Code-switching looks like confusion. Bilingual children often mix languages within a sentence ("I want mas leche"). This is a sophisticated linguistic skill, not a sign of confusion — but it can look like a problem to observers unfamiliar with bilingual development.
What the Research Has Established
- •Total vocabulary milestones are comparable across bilingual and monolingual children.
- •Per-language vocabulary may be smaller, particularly in early years — this is expected and not a delay.
- •Bilingual children show stronger executive function — better attention switching, working memory, and inhibitory control — likely from constantly managing two language systems.
- •Cognitive benefits of bilingualism (executive function, theory of mind, later-life cognitive reserve) are replicated across decades of research.
- •Bilingualism does not cause speech disorders. A bilingual child with a speech disorder would have that disorder in either language.
When a Bilingual Child Has Real Speech Concerns
If a bilingual child has actual speech delay or disorder, it shows in both languages. The right evaluation is from a speech-language pathologist who can assess in both languages (or works with an interpreter) and uses bilingual-appropriate norms. "Just drop the second language" is outdated advice and is not supported by evidence — research shows that simplifying a child's language environment does not help speech delay.
Practical Implications
If you're raising your child in two or more languages — whether by intentional choice or because that's your family — keep going. The cognitive and cultural benefits are well-documented, the apparent per-language vocabulary lag is normal and resolves, and the long-term outcomes favor bilingual children.
For practical strategies, see raising a bilingual child: tips for parents. For the broader language-development context, see toddler language development: the complete guide.