Honestly, If you have your nephew you with you can go to Onslow Beach on Camp Lejeune. He's probably going to want to show you around mainside anyway so you'll already be close. It's right off of NC 172/Sneads Ferry road. You won't hear too many peopel mention it because non-federally employed civilians have not been able to access it since 9/11.
Onslow Beach - MCCS Camp Lejeune
Emerald Isle is real touristy but that may be what you're looking for. Hammocks Beach, in Swansboro is rarely mentioned but is less crowded than other beaches:
N.C. Division of Parks and Recreation: - Welcome to Hammocks Beach State Park
If you don't do Onslow Beach. I'd go with Bogue Banks/Crystal Coast. You have the aquarium, Beaufort Waterfront and maritime museum across the bridge, Fort Macon, plus all of the miniature golf places. Or the Wilmington area beaches, you have the Battleship, and another aquarium at Fort Fisher, plus downtown Wilmington to stroll around. YOu will fight more crowds at the Wilmington area beaches, though. Btw, Bogue banks equal Emeral Isle, Salter Path, Pine Knoll Shores,Indian Beach, and Atlantic Beach with Fort Macon at the Eastern tip.
Crystal Coast NC | Outer Banks