My husband, 21 year old daughter, 6 year old stepson and I saw Ice Age 3 in "2-D" on July 4th. We weren't too sure how the 6 year old would react to a 3-D movie.
A lot of the lines were more adult oriented, that totally went over his head, but the movie was so entertaining that he really never stopped to ask why we were laughing. It was action packed to entertain him, AND us!! NOTHING after the credits BTW!
All in all, I would even recommend this movie to my mother, who hasn't had the chance to see the first or second Ice Age movies.