Went to see "Up" with family members and friends ranging in age from 4 to 44. All of us enjoyed the movie very much, albeit on different levels at different ages! The little ones loved the talking dogs and prat falls, and we oldsters liked the story of the marriage and the more mature humor. (Though I must admit that I loved the talking dogs too).
Please note that if you have a particularly sensitive child, there are some scenes of peril and action in the film that might have them in your lap. : )