How Does Bilingualism Affect Cognitive Skills in Early Childhood?

Last reviewed on October 31, 2026.

Parents tend to hear two opposite messages: that two languages will confuse a child, and that two languages will make a child smarter. The first is wrong. The second is far less certain than headlines suggest. Here is what the research supports, including where researchers still disagree. For wider context, see our overviews of cognitive development and language processing.

Does bilingualism confuse children or delay language?

No, not in the sense most parents fear. Byers-Heinlein and Lew-Williams (2013), reviewing common parental questions, conclude that bilingual children are not confused: infants distinguish their languages early. Bilingual toddlers also monitor and control which language they are listening to in real time, much as adults do (Byers-Heinlein et al., 2017).

A more accurate picture of vocabulary has two parts.

• Total vocabulary is similar. Pearson, Fernández and Oller (1993), comparing 25 bilingual and 35 monolingual children from 8 to 30 months, found no statistical basis for concluding that bilingual children were slower to develop early vocabulary. Hoff and colleagues (2012) found the same for total vocabulary when both languages were counted.
• Each single language may lag at first. In the same study of 47 bilingual and 56 monolingual toddlers from high-income homes, monolingual children scored ahead on single-language vocabulary and grammar. Hoff and colleagues note that bilingual children still acquire each language within the normal range of variation.

The difference can persist into school. In an analysis of 1,738 children aged 3 to 10, Bialystok and colleagues (2010) found smaller receptive vocabulary in English among bilingual children, but the gap was largely confined to words used at home, not school words. A US study of 9- and 10-year-olds also found slightly lower English vocabulary (Dick et al., 2019). This is a result of dividing time between languages, and it is not evidence of a problem with learning.

Mixing languages is normal

Bilingual children often combine languages in one sentence. This is called code mixing. Parents sometimes take it as a sign of confusion, but Byers-Heinlein and Lew-Williams describe it as resourceful: children borrow a word when they do not have it in the language being used. Bilingual adults do the same.

The bilingual advantage: what the debate is about

The idea is that managing two languages exercises executive function, the set of abilities behind attention, self-control and mental flexibility. Because both languages are active in a bilingual speaker's mind, the speaker has to keep selecting one and suppressing the other. The claim is that this practice carries over to non-language tasks.

The case for

Ellen Bialystok is the researcher most associated with this view. In a 1999 study, bilingual preschoolers did better than monolinguals on a card-sorting task that required switching rules (Bialystok, 1999). Kovács and Mehler (2009) reported that 7-month-old infants raised with two languages from birth were better than matched monolinguals at redirecting their looking when a rule changed. A 2010 meta-analysis of 63 studies linked bilingualism to better attentional control, working memory and symbolic reasoning (Adesope et al., 2010). Bialystok and colleagues have continued to argue that bilingual experience reshapes cognition, while acknowledging that results vary (Bialystok et al., 2012; Bialystok, 2017).

The case against

Kenneth Paap and colleagues have challenged the claim directly. Paap and Greenberg (2013) reported no coherent evidence for a bilingual advantage across several tasks, and Paap, Johnson and Sawi (2015) concluded that advantages either do not exist or are restricted to very specific, undetermined circumstances. Publication bias is a major concern: de Bruin and colleagues (2015) followed conference abstracts and found that studies supporting the advantage were the most likely to be published.

Later and larger analyses point the same way.

What can we conclude?

For a child in the general population, the best current summary is that any effect on executive function is small, variable and possibly not caused by bilingualism at all. That does not settle every question. Supporters reply that bilingualism is not one thing: the age of learning, the amount of switching and the social context all differ, and an overall average may hide effects in particular groups. Those are reasonable points to test, but they differ from the popular claim that bilingual children simply think better. Comparisons are also difficult because children cannot be randomly assigned to be bilingual, and bilingual and monolingual families often differ in income, education and migration history.

The findings in infants and preschoolers also come mostly from laboratory studies, and the early childhood period is where the evidence is thinnest. Even Byers-Heinlein and Lew-Williams (2013), writing before the largest meta-analyses, warned that the advantage had been overplayed in the popular press, and that bilingualism is not essential for healthy development.

Are bilingual children more likely to have language disorders?

No. According to Byers-Heinlein and Lew-Williams (2013), bilingual children have language disorders at the same rate as monolingual children, and those with a disorder do no worse for being bilingual. The American Speech-Language-Hearing Association states that bilingualism has not been shown to inhibit language development or therapy outcomes in children with language disorders.

The practical risk is misdiagnosis, in either direction. If a child is assessed in one language only, a normal single-language gap can look like a disorder. Conversely, a real difficulty can be dismissed as “just bilingualism”. Clinicians should assess both languages. If your child seems behind in both, or you are worried, ask for an evaluation and do not wait. You do not need to drop a language, and a professional's advice to do so without good reason deserves a second opinion.

Practical guidance for families

The reasons to raise a bilingual child are family, culture, community and future opportunity. Those are good reasons on their own, and they do not rest on the disputed cognitive claims.

1. Provide plenty of good-quality exposure to each language. Exposure predicts proficiency. Place and Hoff (2011) found that the relative amount of exposure predicted 2-year-olds' outcomes in each language, and that hearing English from more different speakers also helped.
2. Use real interaction. Conversation, books, songs and play with people matter more than language apps or screens alone.
3. Support the minority language. The language used less in the wider community is more easily lost, so it needs deliberate effort from home, relatives, community groups or school.
4. Do not worry about a strict system. Byers-Heinlein and Lew-Williams (2013) describe one-person-one-language as neither necessary nor sufficient. Use a pattern that your family can keep up.
5. Speak the language you are most comfortable in. Parents who speak a language fluently can give richer talk in it. This is our general advice, and it fits the emphasis in the research on the quality of input.
6. Do not panic about mixing. Research on how parents' mixing affects vocabulary is limited and mixed. Mixing is a normal part of bilingual life.
7. Start early if you can, and do not give up if you cannot. Earlier exposure is linked with better accent, vocabulary and grammar, with no sharp cutoff, and older learners can still become proficient with sustained practice.
8. Tell teachers and clinicians about both languages, so they can judge your child's progress fairly.

Finally, ignore products or programs that promise a smarter child through a second language. The evidence does not support that promise, and family and culture are reason enough.