Ember is a film with a spec fic premise -- Ember is an underground city, built so people could survive a nuclear disaster on the planetary surface, and now the power generator is failing, and the inhabitants need to return to the surface. The city planners had, of course, left instructions on how to do this, but these have been "lost" along the way. Introduce our two main characters, two teenagers who are just both beginning their careers in the workforce. Let them make some discoveries, and send them on a chase for the missing information.
This certainly feels like a children's film, not just because the protagonists are so young, but because it lacks sophistication. That's not a criticism, just an observation. Personally, I would've preferred more sophistication, but then the film would've been less suited to its target audience. There were a couple of things that happened a bit too easily along the way, but it was a rollicking good ride for most of the film, and atmospheric as well. A good one for the kids.