You aren't too far away so I say beach! I know NC has several great beaches, but if you want to get a little farther from home you could go to Charleston, SC. It's a wonderful place to take the kids. There are multiple different beaches. You could see a different beach every day. The La Quinta in North Charleston is a decent cheap hotel (Best price can be gotten from rest stop coupon book). If you have tents or a camper the KOAs down there have many amenities. The aquarium isn't too cheap but could be a nice splurge. The kids could go to The Battery and play on the statues. You could go to Waterfront park while there (no cost) and walk around letting the kids play in the fountains while y'all check out the views.
If Charleston specifically isn't for you then you have plenty of other options if you live in NC. Take the kids for a couple days in Bat Cave and Chimney Rock. or go to Lake Lure. Take them Gem Mining which is pretty cheap. There are a ton of options within just a few hours of anywhere in NC.