This is a good point in the final analysis. Except the films actually don't seem to be for kids, really. At least not in the PIXAR sense of movies like THE INCREDIBLES or CARS or the MARVEL movies. I mean, there are probably a lot of parents who absolutely won't let their kids see the films because they have way too much sex and violence for a family film.
I personally think that the real demographic for the movies are more men in their early 20's than teens. But the first movie came out ten years ago, right? I think the audience for the films has gradually moved on (to Marvel movies), unlike the Harry Potter movies where the readers and viewers grew up with the characters.
I think it would be smart to reboot the franchise for a new audience, and - like Star Wars - look at the cartoons that actually were for kids to see how to reframe it for the huge international market that's opened up in the past ten years for family films.