We published two articles on the same question, and they were competing with each other rather than helping anyone. This one has been folded into the fuller version, which covers the same ground with the primary research attached: at what age a child should start learning a second language.
The short version is below. Everything here is covered in more depth, with sources, in that guide.
Is there a critical window for learning a second language?
There is a window, and it is wider than most parents assume. The part that genuinely closes early is the sound system: between roughly 6 and 12 months an infant tunes to the sounds of the languages spoken around them, which is why accent is the hardest thing to acquire late. Grammar and vocabulary stay learnable for many years after that.
Learning two languages does not delay speech. Research published in the Journal of Child Language found that bilingual children reach early milestones such as first words and first word combinations at the same age as children learning one language.
Does the starting age matter more than the practice?
No. The amount and the quality of exposure matter more than the exact age, which is why it is rarely too late to begin. The distinction that does the work is between active and passive exposure: producing the language out loud in a real exchange, versus hearing it in the background.
Practically, that means short conversations in the target language anchored to routine moments, meals, car rides, bath time, and open questions rather than yes or no questions. Fifteen to thirty minutes of genuine two way use on most days, sustained over years, outperforms occasional formal lessons. We set out the numbers in how many hours a week a child needs to become bilingual.
What are the longer term benefits?
Beyond the language itself, growing up bilingual appears to strengthen the connections between the brain regions handling language and those handling cognitive control, with effects on attention and working memory, according to Michigan State University Extension's review of the bilingual brain. The size of that advantage has been actively disputed over the last decade, with several large replications finding smaller effects than the early studies, so it is best treated as a plausible bonus rather than a reason to start.
For the full picture, including what European school systems actually do and why screen exposure counts for so little, read our language guide on when to start.
