We just got back from IOA/US with twin (girls) 9 yr olds, who loved and did everything except the big coasters, and my little boy, who turned 6 while we were there. He liked the following:KONG, ET, NUTHOUSE COASTER, MIB, EARTHQUAKE, BEETLEJUICE SHOW,and loved HANNA BARBERRA (where you get to rescue elroy jetson-- it is a motion simulator that felt REALLY JERKY to me,but he loved it, and there were no scary parts). At IOA, he loved PT. FLYERS, UNICORN COASTER, CAT IN THE HAT, ONE FISH, TWO FISH, DISCOVERY CENTER. The things we tried which I thought were too intense for him were: JP RIVER ADVENTURE,(great ride but big drop in total darkness with trex looming), RIPSAW FALLS,SPIDERMAN (my favorite ride with great effects, but the villains come right at you, very realistic, and a big simulated scary fall), T2, and BTTF (REALLY INTENSE AND JERKY).oh, also JAWS. OUT OF THE QUESTION FOR MY BOY. He did go with us thru twister, but DID NOT like it, and huddled on the floor. The rides he did like, however, he went on several times,so he didn't feel like he missed out on anything. (also, we had FOTL passes with our HRH room key, so there were no lines to wait in, if you wanted to repeat a ride)
hope this helps!!