Ok to start off, this one was so much better than the first.
So they work together a lot, but there is some things that I really wouldn't consider a good message for little kids. (Listen below)
The 'bad guy' picks up Moon and tries to throw him off of 2 high surfaces, clearly intending to kill him, but Moon gets saved both times. The fighting planet, isn't so bad, because the part where they fight is a dance battle.
No 'real' swearing, just uses of the words: idiot, stupid, and at one point, an over dramatic wolf tells Moon and his friends to 'got to heck'. She didn't use the real word, but if I had kids I wouldn't want them to repeat that.
The elephant and gorilla are both pushed into doing something they don't necessarily want to do. The elephant has to dance and kiss a random guy, but during the live performance, she imagines she's dancing with a guy she likes. As for the gorilla, he has to learn to dance from a very mean instructor who does not like him, and it gets to the point, where he has to leave the studio out of frustration.
All in all, I'd say this movie would be fine for a 4 year old that will listen to you when you tell them not to repeat something.
Hope this helped!