
I'm quite familiar with the area. We live in Kennebunkport!
June in Maine can be unpredictable. Sometimes it can be hot toward the end of the month, and other times it can be downright chilly. August is usually very nice, although it can get hot. As far as crowds go, you'll probably see more tourists toward the end of August than the end of June. Both can be quiet, though, because the real tourist season runs from about July 4 to mid-August. The fall gets busy with leaf-peepers.
Schools in our area usually resume after Labor Day, but some do go back the last week in August. Usually the towns that cater to tourism don't go back to school till after Labor Day because so many of the high school kids have summer jobs that require them to work right up to the end of summer.
Kennebunkport is a beautiful little town. There are a lot of very good restaurants in the area- Allison's Restaurant, Windows on the Water, Federal Jacks, The White Barn. For the best fried clams, and other seafood, visit the Clam Shack. It's a small building just before you head over the bridge in Kennebunkport. It's take-out only, but there are some benches outside, or people just enjoy standing on the walkway over the bridge and eating their food.
The beaches in the area are beautiful, also. Like someone else said, only the hearty and brave actually go in the ocean! Kennebunk Beach is a nice place to take a stroll. There's a sidewalk right next to the beach that goes for quite a distance. If you're looking for a beach with more sand and action, try Old Orchard Beach.
Any questions, just ask!