I can understand why a lot of people did not like this, due to several things. It does have a lot of "fake" cussing and sexual innuendos, and does sort of teach that anger is a solution. (Sometimes it can be, and in this case I think was an appropriate response. I was just a little surprised given how it started.) As to whether it's appropriate for kids... I think it depends on the kid and you would have to judge for yourself. Older kids are far more likely to pick up on some things, and very young kids probably won't get it on most of that stuff. The ones in between, depends on the kid. How smart are your kids? Apparently the writer writes for The Simpsons and King of the Hill, so maybe bear that in mind.
I don't have any kids so if I watch a kids' movie, it's for me, and I'm not going to want something that was intended for 5 year olds as that would be boring as heck to me. (I don't assume animated movies are for kids. And I just can't imagine they made this for 5 year olds.) I enjoyed this movie. It wasn't great, but it was pretty good, and many parts were amusing or downright funny. I guess it depends on your sense of humor. I certainly am not going to claim, like one reviewer did, that if you don't think this is funny you've missed all the jokes. That's not true - people have a different sense of humor. My mother would've hated it and thought it was really tacky.
Even though it felt like the movie was saying anger is a way to deal with issues, I was actually happy that it wasn't about dealing with all your anger in a zen sort of way (as the trailer implied). I felt sorry for Red, because there was no excuse for how he was treated, and he was smart and someone who could "see" what was going on most of the time, and it was probably difficult to deal with all the other dippy birds. The other people in anger management class very much amused me. The pigs were well done, though sometimes a bit tacky as well. I loved all the baby birds - they were just too cute. I have a great appreciation for animators in general, and I love when they can make something so cute, or facial expressions that are so right-on. Regardless of humor, subject matter, or whether it's crude - I think it's well animated.
Since so many people mentioned the eagle peeing off the cliff, I guess that's not a spoiler anymore. It was funny, at first, because it was so unexpected. But it just went on for WAY too long and lost any humor. That's one part I did not like. I'm also not sure what politics people are referring to -- I have watched it twice now and still don't get this. Or maybe I was just enjoying it and not looking for politics everywhere.