I think the beach in Ogunquit will probably be packed on July 4th week(end). But, it's a pretty decent beach by New England standards (there's actually sand). There are a few smaller beaches in Kennebunkport, too. But, they're really small and located around the resorts. They'll probably be packed.
The last time we were up there, we ate brunch at Bintliff's Ogunquit. It was fantastic. Probably the best brunch I've ever had and one of the top 2-3 Bloody Mary's I've ever experienced (the best is the B.L.T Mary at Hash House in Las Vegas).