5 is at the younger end of the spectrum, so the kids would need some help from parents, but I strongly recommend scavenger hunts like Sorcerers of the Magic Kingdom (go to the Firehouse in Town Square) and A Pirates Adventure (Adventureland MK, past Pirates of the Caribbean next to the Golden Oak Outpost). Little kids will have a blast using their MagicBands (or keycard) to "activate" all the special effects and special portals, and they loved collecting the cards. Sorcerers is easy (you can hold up literally ANY card, it doesn't matter, so it's not complicated) and can take you all over the Magic Kingdom. Pirates Adventure has 5 different missions, all with really cool special effects. Even better is when random people stop to ask, "How did you do that?" and the kid feels super special. We could have literally spent ALL DAY doing those two games in the MK. Haven't tried Wilderness Explorers yet in Animal Kingdom, but it's another scavenger hunt.
Also, playground-type adventuring always appeals. Tom Sawyer Island is great. My son could have spent HOURS "shooting trains" from the crow's nest rifles. My kids could have bounced across the barrel bridges over and over again. Dumbo also has a nice indoor playground where parents can relax for a while, even if you don't want to ride the ride. The Boneyard in Animal Kingdom is another awesome playground. Too bad Hollywood Studios got rid of their playground.