"I know some children."
Translation:Én ismerek néhány gyereket.
This is indefinite conjugation, (some children, not the children). See here http://www.hungarianreference.com/Verbs/Verbs-Definite-Conjugation.aspx and here http://www.hungarianreference.com/Verbs/Verbs-Indefinite-Conjugation.aspx.
It's wrong. It's true that the emphasis is on the thing in front of the verb, but you cannot just separate an adjective from its noun. "Néhány gyereket" has to stay together. If you put ismerek behind it, it can emphasise either part of that construction. In speech, you can put stress on the specific word you want to emphasise.