A child has in one of the languages he is acquiring. Usually, multilingual children are a bit behind their monolingual peers, but this doesn’t mean that they’ll never catch up. We know from many studies that a bilingual (or multilingual) child knows at least as many words and probably more and at least as many concepts and probably more as monolinguals.
The bilingual could have a higher English (or other language) vocabulary than the monolingual.