Yes you can do it! We actually just did it yesterday 6/18 with my 6yo daughter and 2yo son. We did buy the express passes for IOA and it was worth every penny. Some lines were 60 minutes wait and we got on with our passes in no more than a 10 minute wait for every ride. The 10 minute wait was for Dueling Dragons, the wait for non-express was 60 minutes. DH rode spiderman, the line was out the door and he walked right on with his pass. Also with the Hulk the line was sooooo long and we got right on. It was really great for the kiddie rides also. Got right on with all of them. I dont think we could have done it all if we didnt have the Express pass. What we did is US first, got there before it opened. It didnt really get crowded until about 12. So we did everything there, rode a lot twice. Definitely didnt need the express there so I was glad we didnt buy it for both parks. Then went to IOA and thats when we had our express passes. We bought it on the universal website. With little kids it is definitely worth every penny.