Universal Studios(US) - they have reopened Curious George (CG) since my last trip in April.
Some elements in CG may be a little too intense for the 3 year old, as there are buckets of water coming down from the second floor above, as well as people with water cannons trying to hit him if he tries to go from the front of the attraction to the area where there is a two story (dry) ball shooting arena.
But I would think both would enjoy it if you set the 7 year old loose to get wet, make others wet, and enjoy the game ball arena, while walking what I call the "Parent path" to take the three year old on a romp through throwing, figuring out the "Vacuum" ball, gather ball in net bag and dump, & "Shoot"ball sequence on the second level, while being able to keep an eye on DS1 (Dear Son, oldest) darting in wet.
Have to tell you, I think you must be a great mom to take on a visit to two major theme parks without help - have you considered taking along a family member or friend to help?