I recently watched this movie with my 3 and a half year old. The parts that were mutually enjoyable were the traditional slapstick animation moments. They are almost too exciting for someone so young, and I caught her covering her eyes once when an animated character was trying to outrun an avalanche. There are very few movies for little ones that don't feature explicit scenes of violence and death. In this movie there are some fight scenes, but no creature dies on screen. After seeing Atlantis,and the death toll extracted before the closing credits, this is a refreshing change.
I agree with reviews about the lack of smoothness in the animation of this film. This is especially evident with the Neanderthal characters. I did think that the various textures of snow, ice, mud and fur were well rendered. The story line plods along to a predictable conclusion. This is a family film that will be more enjoyable for the smallest viewers in your household than for the adults. But, adults have so many entertainment choices, that it's nice to a movie something that can be shared. Younger viewers will be able to follow what is going on without a lot of explanation from adults.