It's not just the young folks who get trapped in fantasy ideas about magic. I see plenty of those that are older that are just as guilty of not being able to understand that film magic might not be the same as real magic. I don't think it's fair to imply that it is only the younger members on here who ask foolish questions or expect this to be like Harry Potter.
How do I deal with them? I try to educate them as to what real magic is all about. I explain when something isn't possible, I offer resources for them to study, and (at least in regards to Wicca) I share with them what I have learned in 30 years of practice. I do this because many of the ones asking these questions are simply misinformed, not ignorant. They can learn and grow given proper support.