I'll second that about Assateague. IMHO, not the best beach for little kids though. The dropoff to "over kids heads" water depth is sharp. We couldn't relax on the beach for watching the kids all the time.
If you camp the horses WILL come visit you. We had them standing right on the light-line caused by the coleman lantern when we went. One came right up and made a grab for a pack of hamburger buns that we had on the table...until my wife punched him in the nose that is.
Also saw quite a few sitka deer.
Well worth the trip. Good fishing would be a bonus.