My daughter was on Humira for about two years. It took a while to work for her and didn't really kick in until we added methotrexate (but it's not that way for everyone, don't worry!), but once it did, it was wonderful! She was like a normal kid again. She didn't get more infections with usual and we didn't really have problems with side effects. The shot is quite painful though and difficult to get used to. We always iced before it, but it still hurt quite a lot. She's older though, so she was willing to put up with the pain to have a pain-free week.
Good luck!