Well, I think "young" is subjective... I've seen children who were at least 5-6 years old with pacifiers, and possibly older, which I would classify more as "children" rather than "young children"... but you're right and the question should be reworded
how about "How old does a child have to be to start using a pacifier?"
although that doesn't really address the other part of his question (should pacifiers be used)