Love NJ beaches, as I grew up on them every summer as a kid. When our kids were young, we went to Cape Cod every summer. Lots of great places to stay there but it’s likely that many of the most desirable places will already be booked.
Kiawah Island is beautiful but there is not a lot, other than the beach, to do there. The Sanctuary is a gorgeous resort, though, if you decide on Kiawah. There are rooms, villas, all beachfront, and a lovely spa.
Hilton Head is wonderful year round and very popular in the summer. Beautiful beaches, hundreds of restaurants of all kinds, shopping galore, antiques, art, a great theatre for live productions. movie theatres, 55 miles of bike trails, boating, kayaking, nature preserves, dozens of golf courses, tennis, fishing, zip lines, outdoor concerts. Lovely historic towns close by - Beaufort and Savannah. Charleston is 1 1/2 - 2 hours away, an easy day trip, where there’s a terrific aquarium, in addition to all the beautiful architecture and other things to do there. Lots of homes, villas, condos to rent, and lots of nice beachfront resorts.