If you travel to Myrtle Beach in South Carolina, you can go to the Family Kingdom Amusement Park. They have a water park, various rides, games, slides, and a Ferris wheel with an ocean view.
Hilton Head biking trails
Biking is one of the best family activities on Hilton Head. Rentals are cheap, the biking is relaxing and is frankly just good old fashioned fun that isn't manufactured. Don't expect to find racing bikes or mountain bikes zipping around the trails. Just simple beach cruisers you can rent about anywhere.