I havent been to IOA but Universal has great stuff. When we went with my nephew and niece last time they could pretty much ride everything. Like metro said it depends on what your kids like and how tall they are could play a factor as well if the 9 could do the rollercoasters it may be enjoyable for him. I think over at Universal they would rly like MIB it seems like a perfect kids thing and you can do most of the raids with the full family as they are more showy. I have yet to ride the mummy and hoping to do that next weekend when I go but your 2 older kids are probably old enough if they like coasters also.