Welcome to Maine.
As you said, kids that age want to go to fun places. I would suggest Old Orchard Beach....... Seven miles beach, amusement parks, water slide parks etc etc.
Close by, is York with the animal kingdom, and fun rides. Our favorite campground is Hid'n Pines which we have a site reserved the first week of July year after year. There's a shuttle bus that brings you to the beach and a grocery store is conveniently located next to the campground.
Don't get me wrong.......I love Acadia National Park(we go there every year), but with the ages of your kids (5 and 2), you probably will end up carrying them.