You can't deny Harry Potter was a series started for and specifically aimed at kids/"young adults," even if the appeal has spread. A G rated movie is always advertised as a family film, but typically it's just for the kids.
Harry Potter has done wonders to get kids to read, although I can't tell you how annoyed I get when I hear people talk about reading and say things like "Oh yeah, Harry Potter is so great! I don't read anything else, though." There's a lot out there, and plenty of it is as good or better than Harry Potter, and while I'm sure plenty of kids will find that out, a lot of them won't. Lord of the Rings is literature, and its influence and complexity really isn't comparable to Harry Potter, except maybe in the category of pop culture.