My son is 5, we have been pumping for about a year and a half. He has the Animas Ping and uses the Inset 30 sites. The cannula goes in at an angle - we picked it because my son is thin and doesn't have a lot of fat to put sites into.
I always use an alcohol wipe to prep the sites. I also was using IV PREP to help with stickiness but certain lots of that are recalled, so for right now, I'm just using the alcohol wipe. The sites usually last 3 days. I usually just peel it off (like a bandaid, go fast!) I used to use some adhesive remover and while it did let the site peel off pretty quickly, it seemed like it left the adhesive on his skin and he'd get a big 'fuzzy' patch on the old sites. You can wipe off residual adhesive with an alcohol wipe, but I find if I just peel the site off, I don't have to do that. I don't notice much of a difference in andhesion right now, but it isn't summer so my son is not getting very sweaty or wet on a daily basis. :)
When my son complains that a site is hurting, I usually will check for a problem. If it is right after I put it in, I wait for a while, it can hurt some when it goes in. He often says that it hurts at first and then it goes away. If after a day or so, if my son says his site is hurting - especially when insulin is given (like for a meal) then I change the site right away. It has meant in the past that the site is getting infected or there is some other problem with it. I have found it will get worse, so just change it if it starts to hurt.
I also am finding we have fewer problems with sites on his backside than on his tummy. Again, he is really thin, so his tummy sites are tough because I feel we are only going into skin, there is little if any fat. On his butt, I think it goes into some fat and he seems to handle it better.
Good luck, it will take a little while to be really comfortable with the pump, but it is such a blessing for us. (Also, if you haven't already, check out the Tummy Totes from tallygear.com. They are great for active little boys (and girls!) to keep their pumps concealed and out of their way. :)