We took our 3.5 year old today & she really liked it!
That being said, there were some parts that scared her a little bit. This wasn't her first movie, so I think that helped with the nerves (wasn't scared of the dark or anything). Some of the parts with the bears, especially Mordu, were a little intense. At one point she said, "mommy, that was scary" and she sat in my lap most of the time, but other than that she was fine. Towards the end when there were more bear parts, I'd talk to her in her ear about what was happening, "ooh, ________ looks mad" or "do you think _______________ is going to win?"... stuff like that.