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Presumably you are asking if the speech of "bilingual" children is slower to develop than the speech of those who speak just the one language. If I have interpreted the question correctly and I apologise if I haven't, I would suggest that the speech of "bilingual" children would be slower to develop purely because of the "volume" of words that they would have to learn! However I should think that if they have the ability to learn two languages at the same time the delay in progress would be very little.
The question is grammatically incorrect.
