Chincoteague is fun for the kids, but will probably be warm, but hey, it's summer and it can even be hot in Maine in the summer, but a drive up to Acadia with stops at some of the southern ME beaches might be nice.

Have you considered your home state? Perhaps up to Lake George with stops at Saratoga for the battlefield NP or to Lake Champlain with a ferry ride over to Burlington VT?

You do not want to do Williamsburgh in Aug - we were ther for a few days in July and it was almost 100 and humid. I would save that for Oct - or May.

Have you looked at staying closer to home? When I was a child my family always took a cottage in Sag Harbor for a couple of weeks. Right on the bay but easy access to the ocean. Lots of cute small museums and other activities (whale watching, fishing from Montauk, crabbing etc). Parents broughg out bikes so we could wander around locally on our own. (Must admit part of the benefit was taking the dog along -a nd often cousins would come and take a nearby cottage.) And onthe way you can see Old Bethpage Village, Air and Space Museu in Westbury, Teddy Roosevelt''s House in Oyster Bay and the entire noth fork - as well as shelter island.

When my kids were younger we went to Chincoteague every August for about five years. Needless to say it was a big hit. We always rented a house and I think to get the 'best' deals we put in our reservations right after the first of the year when the season's listings came out. I don't ever remember the heat being an issue. It's an island with a beach - and lots of shade. The kids loved the ponies. Have they seen/read "Misty of Chincoteague"? We did do day trips to Williamsburg a few years, also took a boat over to an island in the middle of Chesapeake Bay (name escapes me at the moment) where there is a small fishing community that's has been relatively isolated there for the past few hundred years. Some years we combined Chincoteague with a few days in DC. Once we stopped at Wintertur Garden - more for me than the kids but they had a good time.

In August I think you have to head north. Nantucket? Maine?

Have you ever heard of Lake Wallenpaupack in PA?
http://www.homeaway.com/vacation-rentals/pennsylvania/lake-wallenpaupack/r8241
It should be a little cooler than an open beach.

Adirondacks?


http://adirondackrentals.com/

Last week in August is still free in this beautiful house on a lake:

http://www.homeaway.com/vacation-rental/p103436

I know you're posting in the US forum, but what about heading north to Canada - e.g., Quebec, Ontario, Prince Edward Island, etc? You could drive to southern Quebec or Ontario, and do a combination of northeastern US and southern Canada.

Currently, Porter Airlines (it's hard not to like an airline that has a beaver as a mascot) is offering 50% off its base fares for bookings through early September. So you could get flights for about $300 per person to Montreal, then rent a car and explore Quebec. Tons of history, beautiful scenery (lots of options for hikes etc), a taste of French culture, and good food. You can visit the oldest walled city in North America (Quebec City), find great bagels and jazz in Montreal and, in between, hike and spend time by the water.

Have you thought about San Diego? There's the beach, there's an amazing zoo and Sea World, there's Legoland. Also, there's history with the missions and downtown San Diego. It will be hot, but it's not humid out west. Plus, it sounds like your family has never been there.

A cottage on Lake Winnipesaukee in NH (there's also Lake Winnisquam and other lakes). Kitchy = Weirs Beach area on the southern shore. I would choose something in the Moultonboro, Center Harbor, or Wolfeboro area on the northern side which puts you that much closer to the mountains for all the tourist attractions there. Educational = Squam Lakes Science Center. Canterbury Shaker Village and Portsmouth's Strawbery Banke could be day trips. There's three summer theaters in the area. There are lots of events in August.

frogoutofwater--that mascot of Porter airlines is a racoon, not a beaver. A nice airline, and love your suggestion of a trip to Canada. Don't forget your passport.

Chincoteague shouldn't be overly sticky. Now, I like it hot, but I've found it overly cool, even in the summertime. CW, on the other hand, will be pretty warm and humid, although I've done it in the summer and lived to tell the tale, and it makes pools and waterparks highly appealing.

Any beach destination on the East Coast (above Myrtle Beach anyway, GA and FL will be pretty darn warm even on the coast) shouldn't be ridiculous in August, but it might not be the best time to visit unairconditioned historical things.