We've been to Acadia twice over the past 10 years, and love it. Stayed in Blackwoods campground - no hookups, but campsites are great and location is wonderful.
Acadia is all about bicycling, hiking, and scenic views. We love it, and plan on going back. When we went, our kids were teenagers, all very much into the hiking and biking, and they loved it.
I sort of hesitate to recommend Acadia to under 10 year olds... depends on your kids how much they'd love it. I would lean towards staying in a full hookup campground with some kids activities, and then go into Acadia for a few short explorations.
Thunderhole is cool, especially if it is wavy when you are there. Cadillac Mountain is really neat - we've been up there at sunrise which is really neat, but again young kids may not be as impressed. If you go for sunrise, bring warm coats! Even in summer it can be windy and chilly (if not cold) up there!
You may find you want to return to Acadia when the kids are older and really explore the hiking and bicycling trails.