As someone who has taken his kids to many theme and amusement parks over the years, a playground in the park is a godsend. Kids aren't going to spend their entire day there. But an hour where they can run around and blow off some steam on a day where we dragged them out of bed early to stand in the line for the bus from the hotel to the park, to then stand in line to get through security checkpoint, to then stand in line waiting for the gates to open, to then stand in line for every ride, show, and churro stand, all while sights and sounds and smells and other sensory inputs are blasted at them everywhere they turn, is essential to help prevent meltdowns (both for the kids and parents). One parent, or a grandparent, can sit with a coffee and watch them while the other parent single-riders a favorite ride. Then they swap duties. After 45 minutes to an hour, the kid(s) are ready to do something else.
Slow, boring, unpopular rides you might not otherwise ride like a train ride, PeopleMover, Living with the Land, or Fast and Furious Supercharged are great for combating sensory overload as well.