In DCA, If your child likes Disney Jr, the Disney Jr Dance Party is a lot of fun, multiple shows throughout the day. It's Tough to Be a Bug is also fun and never a wait.
In DL, the Mickey and the Magical Map show is fun, several shows throughout the day Friday through Monday only (in the theater over between IASW and Toontown). If your child likes Star Wars, the Star Wars Launch Bay is cool and you can meet Darth Vader, Kylo Ren and Chewbacca. You can also participate in the Jedi Training (must sign up in the morning) or just watch, it's fun to watch and kids watching can all sit down in the front. It's always fun to ride the train if the wait isn't too long... Tomorrowland station seems to usually have the lowest wait. We enjoy taking a trip around the river on the Mark Twain or Sailing Ship Columbia or try paddling the canoes. My son also likes riding the Main Street vehicles, especially the horse-drawn car.