>Asking them to clarify their question either highlights that they actually have no clue what they're looking for

That wouldn't be very nice towards them, though. Many times children ask questions not because they're interested in their particular questions - quite often they don't really have a clue of what they're asking, as you mentioned - but they ask for the sake of learning something.

At least, that's the usual answer to "why children ask so many questions": because they like to learn, more than because they have a specific question.