Nags Head is a barrier island on North Carolina's Outer Banks with the Atlantic on one side and the Roanoke Sound on the other. The beaches are wide and uncrowded. The water is warm by Mid-Atlantic standards. The town runs along a single road, so nothing is more than a 10-minute drive — easy for grandparents who don't want to navigate, and easy for the parents who'd rather not.
The sound side, where The Village at Nags Head sits, gives you calm-water sunsets, kayaking the whole family can do, and the protected piers and parks where toddlers can wander safely. The ocean side gives you the classic OBX beach day. You can do both in the same afternoon.
And critically — Nags Head has the infrastructure multi-gen trips actually need: grocery stores (Food Lion and Fresh Market are next to the Village), pharmacies, a hospital in Nags Head proper, family restaurants of every speed, and activities that span the age range from 3 to 83.