I've been watching this with my 5-year-old and find it's watchable by both adults and kids. The writing and dialog aren't wooden or simplistic. Although it's not at the depth of an Aaron Sorkin show, there is intrigue and nuance in the conflicts between Aang and his adversaries as well as among the adversaries themselves.

It's this kind of writing that can absorb and involve a first-grader yet not drive his parents up a wall that makes this more interesting to watch than say a "Fairly Odd Parents" or Disney's "Aaron Stone". These are writers/creators who trust their audience to "get it" and who try to keep things accessible without talking down to the audience. That takes both talent and skill.