The "bilingual delay" idea has been studied repeatedly and does not hold up. Bilingual toddlers hit speech milestones on the same timeline as monolingual ones when you count words across both languages combined. Here is what the research actually shows and the strategies that work.
If you're raising a bilingual toddler in the US, you've probably heard some version of "speaking two languages slows them down." The advice usually comes from well-meaning relatives, sometimes from older pediatricians, occasionally from preschool teachers. It is wrong, and the research is unusually clear about it.
Here is what's actually going on.
Studies comparing bilingual and monolingual toddlers consistently find:
The "delay" myth comes from counting only one language. A child who knows 30 English words and 30 Spanish words has roughly 50 unique concepts (some overlap) and is at the 50-word milestone. Counting only English would suggest delay; counting both shows typical development.
The CDC milestones can be applied to bilingual toddlers by counting all words across all languages:
If the toddler combines words across languages ("mama agua" or "more papa"), that still counts as a combination. The brain understands the syntactic structure.
Each parent consistently speaks their dominant language with the child. Most-studied approach. Strong outcomes when consistent.
Works best when both parents are fluent in their assigned language and consistent. Doesn't require strict adherence — occasional mixing is fine.
One language at home, another at school/daycare. Or one language on weekdays, another on weekends. Works well in households where one language has a dedicated context (grandparents who only speak Spanish; immersion preschool; etc.).
Family speaks the minority language at home; majority-language exposure comes from school and community. Useful when one language is at risk of being lost.
Caveat: this approach requires intentional effort. The dominant culture's language will dominate without protection.
The biggest single predictor of vocabulary in either language is being read to in that language. 10-15 minutes per day per language, ideally.
The milestone tracker has a custom-vocabulary log so you can count total words across languages — the right way to track bilingual milestones.
Open the milestone tracker →Code-switching ("I want my zapatos") is normal. It is not a sign of confusion. Bilingual brains process both languages constantly and pull from whichever has the most accessible word at the moment.
By age 4-5, most bilingual children can keep languages separate when needed (e.g., speaking only Spanish with grandparents who don't speak English). Before age 4-5, mixing is typical and expected.
If your bilingual toddler is missing milestones across BOTH languages combined:
That is potentially a real language delay — not a bilingual effect. Call Early Intervention. Bilingualism does not protect against actual language delays, and EI services can work with bilingual families.
Some older pediatricians or speech therapists recommend dropping a language to "let them catch up." The research firmly contradicts this:
If a clinician recommends dropping a language, get a second opinion from a bilingual-experienced specialist.
General guidance. Bilingual-language concerns should be evaluated by a speech-language pathologist with bilingual specialization.
