Does raising a child in two languages cause speech delay?

No, according to King and Mackey, the authors of The Bilingual Edge. Their position is that bilingualism does not cause speech delay or any other developmental disorder. They base it on a study that found children learning two languages on the same vocabulary timetable as children learning one. If something about your child's talking worries you, ask a professional to look at it; the note below says how.

What the sources say

King and Mackey say delay is one of the two worries they hear most often from parents; the other is mixing the two languages. Their own summary of the chapter is a single line: bilingualism does not cause speech delay or any other developmental disorder.

Their evidence is a 1992 study by Pearson, Fernández and Oller, as the book describes it. We read the book, not the paper. The study compared children learning English only with children learning English and Spanish, using the same vocabulary questionnaire. Both groups followed the same timetable, including the timing of the vocabulary spurt, and by school age the bilingual children's combined vocabulary matched or exceeded that of their one-language peers.

Why it can look like delay

A child learning two languages knows words in each of them. If you count one language only, you see part of what the child knows. King and Mackey say a smaller vocabulary in each language taken separately is normal at an early age and typically closes by school age. The study above counted both languages together.

Quiet is a different case. A child who goes quiet in one language, especially after a big change such as a new class, a new caregiver or a move, may be in what King and Mackey call the silent period: a normal, active stretch in which the child takes in sounds, words and grammar without saying much yet. Their guidance is not to push for speech. Pressure tends to add anxiety, not speed. This describes silence in one language after a change. It is not a way to judge whether a child's speech overall is on track.

What to do tonight

• Keep talking, reading and singing in both languages, at the same quality and quantity as before. Do not drop one to be safe.
• Do not push your child to speak before they are ready.
• Write down what worries you in concrete terms: which words or sounds, in which language, since when. A specific description is easier for a professional to use than "he talks late."
• If someone tells you to drop a language, ask what exactly worries them about your child and how they think it connects to having two languages. King and Mackey say no sound research supports dropping one, and that the two are sometimes assumed to be linked when they are not.

What is still unknown

The sources read for this site give no ages or milestones for when a delay is worth worrying about, and none says how to tell a child who is simply a late talker from one who needs help. So this article names none. King and Mackey also say very little research exists on special needs and bilingualism specifically.

When to ask a professional

Ask whenever you are worried. Hearing, speech and development are for your child's pediatrician or a speech-language therapist to assess, and this article cannot do it.

If your child has an identified need, King and Mackey note that the common advice is to switch the family to the majority language. They say it is not reckless but is not backed by much research, and that professionals trained to look closely at one skill often have little time to weigh the whole family. Their suggestion is to talk through what a switch would cost, for example the chance to talk with a grandparent who does not speak the majority language, together with the people already working with your child.