Myths about raising a multilingual child, checked against the research

17 October 2026 · 6 minute read

Most of what worried relatives say about raising a child with several languages is wrong, and a couple of the cheerful claims you'll read online are shakier than they sound. Here's how the common beliefs hold up against the best studies we could find, with the strength of the evidence spelled out.

"Two languages will confuse a toddler"

This one has the least going for it. Babies can tell languages apart within their first days and months of life, which is why researchers who advise policymakers argue against holding back a second language for fear of confusion (Fibla and colleagues, 2021). Toddlers who mix words from two languages in one sentence are simply using every word they own, the same way bilingual adults do (Byers-Heinlein and Lew-Williams, 2013).

"Bilingual kids talk late"

They don't, on average. In a comparison of 302 Polish-speaking children growing up abroad with a second language and 302 matched children in Poland, both groups said their first word at about 15 months and reached ten words and first word combinations at the same ages (Muszyńska and colleagues, 2025). The belief survives because people count only one language. At 30 months, 47 Spanish and English toddlers knew about 580 words across both languages, against about 540 English words for 56 English-only toddlers (Core and colleagues, 2013). We go into this properly in our post on bilingual toddlers and late talking.

"Drop a language if your child is slow to talk or gets a diagnosis"

This is the myth that does the most damage, because families act on it and it usually means a parent stops speaking their own language to their child. Reviews find no evidence that more than one language harms autistic children (Gilhuber, Raulston and Galley, 2023), and for children with a developmental language disorder, therapy in both languages helps the second language as much as therapy in the second language alone while also supporting the first (Harvey, Allaway and Jones, 2018). Researchers summarizing the field call the one-language advice for children with developmental disorders unfounded (Fibla and colleagues, 2021).

"If you mix languages, your child will mix them up"

The evidence here is genuinely mixed, but it leans toward relax. A 2026 synthesis pooled seven studies covering 541 children and found that parents' mixing had no relation to how well children spoke either language, with at most a negligible to small link to understanding the majority language (Verhoeven and colleagues, 2026). A separate study of 52 Polish and Turkish children in the Netherlands did find that more parental mixing went with a smaller spoken vocabulary in the home language, yet its authors explicitly don't advise parents to separate their languages strictly, since they can't tell which way the link runs (Verhoeven and colleagues, 2025). If you mix a lot and your home language is the fragile one, giving it some unmixed time is a reasonable hedge.

"You need one parent, one language"

It's a fine system, and it isn't required. In De Houwer's survey of 1,899 Belgian families, children were actually most likely to speak the minority language when both parents spoke it at home, and the paper concludes that one parent, one language was neither necessary nor sufficient (De Houwer, 2007). A Dutch study of 136 families found the family pattern stopped mattering much once researchers counted how much of each language children actually heard (Verhagen, Kuiken and Andringa, 2022). Amount and quality of input beat the label on the system.

"Speak the local language at home so they're ready for school"

For parents speaking a language they learned late, this tends to backfire. Mothers with limited English talked as much as native speakers but used sentences about a third shorter and about 40 percent fewer different words (Hoff, Core and Shanks, 2019), and in a Dutch study of 50 preschoolers, it was the fluency of the non-native speakers, rather than whether a parent was native, that predicted the children's Dutch (Unsworth and colleagues, 2019). Reading at home in the home language even helped preschoolers learn English words as well as reading in English did (Roberts, 2008). The full argument is in which language to speak to your child.

"Three or four languages is too many"

There's less research here, and what exists is reassuring. In Montreal, 20 trilingual toddlers knew somewhat fewer French and English words than 170 bilingual toddlers, a gap that wasn't statistically reliable and that the authors put down to the trilinguals simply hearing French and English for about 73 percent of their day (Côté, Gonzalez-Barrero and Byers-Heinlein, 2019). Their third language wasn't even counted. The real constraint is hours in the day, which we work through in our post on raising a child with three or four languages.

"A video or an app can teach the language"

On its own, much less than you'd hope. Nine-month-olds learned to hear Mandarin sounds from about five hours with a live speaker and learned nothing measurable from the same amount of Mandarin on video or audio (Kuhl, Tsao and Liu, 2003), and a meta-analysis of 59 reports puts the average video learning gap at about half a standard deviation for children up to six (Strouse and Samson, 2020). We make a language game, so we have every reason to say otherwise, and we still think a grown-up next to the child is the part that does the teaching. More in what toddlers actually learn from screens.

"Bilingualism makes children smarter"

This is the cheerful myth, and it's mostly a myth. The claim is that juggling languages trains executive function, the mental control behind attention and switching tasks. A 2021 meta-analysis of 23,414 children found a tiny advantage for bilinguals that shrank to nothing once the researchers corrected for the tendency of positive results to get published (Lowe and colleagues, 2021). A separate meta-analysis came out with a similarly small average effect, signs of publication bias, and little support for an overall advantage (Gunnerud and colleagues, 2020).

That's fine. The good reasons to raise a child with your languages are the people and places they open up: grandparents they can talk to, the books you grew up with, and more than one place that feels like home.

Keep reading

Is my bilingual toddler a late talker? What the research says

Worried your bilingual toddler is talking late or mixing languages? Research shows bilingualism doesn't cause speech delays. How to count words across languages, and when to get help.

Which language should you speak to your child? Usually the one you speak best

Should you speak the local language to help your child at school? Research on parents speaking a second language, native versus fluent input, and where the community language really comes from.