IOA has Suess Landing, which has four rides for all ages, and an interactive play area. Toon Lagoon has a play area, Jurassic Park has TWO play areas (Camp Jurassic, and Discovery Center) as well as a small kids coaster. Lost Continent has a small coaster, and has loads of fun stuff to look at.....
USF is full of fun things for the little one, including the precious stuffed head characters that roam around, as well as face characters.....though your little one will have no clue who they are.....still fun. Physically your little one can go on just about every single attraction with a few exceptions (MIB Mummy) Emotionally, that is a different story. You will have to judge what they can handle, though my now 6 yr old loved every single ride she could go on (she was 2 at the time). Dont be overprotective, but if your little own looks like she's going to crawl out of her skin, most likely best to walk away.