Look at Timberlake for your son and Indian Brook for your daughter - both at Farm and Wilderness. Great camps that provide unique experience for each kid and an easy drop off for parents.

If you want rustic, traditional camp, check out Wavus/Kieve in Maine. Separate gender sister/brother camps focused on outdoor activities and overnight hikes.

Camp Moosilauke for boys is terrific.

Bump

I spent my childhood (from 6 years old onwards, then became a counselor) going to a brother-sister camp called Forest Lake Camp in the Adirondacks. Foundational experience and still one of my favorite places on earth. Tons of activities, it's on a private lake- in a beautiful setting. Somewhere between rustic and nice-- nice cabins, but no AC for example and no pool (but amazing lake). https://forestlakecamp.com/

Not sure if Maine is too far, but some family members who went to Camp Timanous in Raymond, ME had really fantastic experiences there. They're still friends, as adults, with people they met there, and talk about the positive development they got from going. It's a traditional summer camp, 7 weeks in the woods, archery, canoeing, etc.

Anyone have a recommendation for a single gender sleepaway camp (either boy or girl, looking for one of each), preferably in the NE

Rustic is good