One of the most common myths about bilingualism is that bilingual children “learn to speak later” than monolinguals. I’ve heard it, read it, said it, but strangely, I haven’t experienced it at all with my three bilingual kids. Now, as a researcher, I know that three kids does not a “reliable statistical study” make… but certainly anecdotally, I have not found this to be the case. In addition, although I’ve heard this myth a lot, and read it in several popular books, I’ve never seen convincing research on the topic. Well, convincing research is on its way, and it comes down firmly on the side of “myth” (for now, anyway!).
This article does a good job of explaining the evidence, and refuting the claim of later language for bilinguals. As an aside, Annick De Houwer’s books are a great reference for parents of young simultaneous bilinguals, although they are definitely “research reading” and not “easy” reading.
From the Linguistics Research Digest Blog:
Do children hearing two languages acquire language at a slower rate?
on raising bilingual children 
I have also heard this myth many times and it has frustrated me to no end. My daughters were raised trilingual and started speaking faster than many of their monolingual classmates. Thanks for sharing this information. I am so happy to put that myth to bed!
I had heard the myth too, but like you, my experience didn’t support it. My daughter began speaking on the earlier side of average, and always had more words than average for her age. Thank you for sharing that study, it looks quite interesting.
My whole family in the UK are from a bilingual background – I don’t think anyone’s ever noticed any of the kids learning to speak slower than our monolingual family friends’ kids. Strangely enough though, I’m pretty sure I’ve repeated that myth myself too!
Myths… who cares about them? All my three bilingual kids (English & Polish) have started speaking rather earlier than their monolingual peers. I know some bilingual families (Polish & German, Polish & Czech) and none of them could support that myth…
This is a frustrating myth that seems to be accepted by so many. My three children experience a fully English environment in the home and fully Japanese environment at school and outside the home. My oldest (8 years old) and youngest (3 years old) speak comfortably and fluently in both languages, switching back and forth as necessary. They experienced absolutely no delay in speaking either language. Meanwhile, my 5 year old is experiencing speech and language delay in both languages, but his delay in English is more significant. I have expressed concern to his teachers and doctors for over two years and I always get the same answer, “It’s difficult for children to to learn two languages. A delay is to be expected.” Because of his bilingualism, no one seems to take his language delay seriously except for me.
Yes, it is frustrating that this myth persists, especially as we can look to bilingual communities all over the world and easily see that it isn’t true. Are you getting speech therapy for your son? I always tell families that speech/language support is a good thing, even if the therapist doesn’t know anything about bilingualism – the strategies they use for language development are helpful, and you can find out what they are doing, and use the same strategies in the home in English. Good luck!