Kids will enjoy this, but it's not a kids' movie
First, regarding this film's appropriateness for kids: there's some violence and death, mean-spirited human characters, and a self-absorbed father who barely notices his own son. Those things -- while not excessive by any means -- might upset some sensitive young ones, but there's enough broad comedy and human warmth to engage most bright kids. However, though kids are welcome, this is absolutely a movie for grown-ups. The dialog is cracklingly brilliant throughout, and the voice performances -- recorded with the actors in the same room, rare for modern animation -- are pitch perfect. The wit is so pervasive and subtle that I found myself quietly giggling practically from credits to credits. Anyone familiar with Wes Anderson's other movies will recognize his touch in the eccentric family dynamics and front-and-center neuroses of every character. The stop-motion animation seems jerky and primitive at first, but as you watch, you start to realize how astoundingly vivid and detailed the sets and characters are. By then end, Mr Fox was as real to me as George Bailey or Charles Foster Kane... but a heck of lot more fun. No way around saying it: this is a FANTASTIC movie.