It depends on the content in the story. If it may be appealing to a younger audience (children), then it’s for children. However, if it seems more in the sense of appropriate for teenagers, then definitely Young Adult. I don’t think that helped that much.
Well, here’s an example that could help:
Harry Potter (the first few books I mean)- children
Twilight- STRICTLY Young Adult
~ Lauren a.k.a. The Prodigy