and spend a good bit of my life at the Delaware beaches. My aunt used to own a large home on the beach in Lewes, and if I could pick one place on the East Coast to retire, it would be Lewes (though I could never afford a place on the beach).
Keep in mind that Lewes is on the bay and Rehoboth is on the ocean. The bay is much safer to swim in for smaller children, but the big kids like the ocean waves. Lewes has a really nice, quaint downtown area, and Rehoboth has all the typical beach town stuff. I spent a lot of time walking the boards in Rehoboth and really miss is now that I live in North Carolina. (If there are beaches down here like Lewes and Rehoboth, I haven't found them yet.)
These two towns are so close together that restaurants and shops are easily accessible from either direction. However, the traffic on Route 1 is really heavy during the summer months. I spent 20 or so years of summer months living on the Rehoboth Bay, and we avoided going into downtown Rehoboth as much as possible (but after you've been there a while, you kind of know what times of day/night are better than others for traffic).
For school information, check
GreatSchools - Public and Private School Ratings, Reviews and Parent Community.
As with any beach town, there are lots of year-rounders and lots summer rentals. You just can't avoid the rental homes no matter where you are near the beach. Renting is a great idea. It'll give you a chance to check out the areas and see what fits your family's needs best.