There are several studies that show that bilingual children have a smaller vocabulary in one of their languages...
compared with their monolingual peers in that language. But if you look at both languages of a bilingual child together...
you will see that there is no difference anymore.
So it shows that bilingual children usually have as many words in both their languages, as their monolingual peers have in one language...
if they are comparable on different kinds of background variables. However, I am not saying it will never be a problem...
because a child must know the words that he or she needs to function at school.
So it’s important that the child will learn these words, but it’s not a reason not to raise a child bilingually.
It’s even an advantage that a bilingual child is able to name things in different languages in different ways...
because languages differ a lot. So, the world can sometimes be different than how you might at first have thought.