Welcome to the community, OP!
I think your son will find the school to be very welcoming, and every year (in every grade) there are new students, so he won't be alone in that regard.
As for summer camps, the most intensive weeks for camp tend to be in June and July, and many options peter out in August as more people go away on vacation. Also, there is no "one" place where Wood Acres kids go to camp, so you're likely to encounter kids from many different schools at any summer camp your child attends.
There are some tennis camps at the private Landon School that run deep into August, which may attract a few Wood Acres kids.
https://www.landonsummer.com/page.cfm?p=4747
Many Wood Acres families also go to Mohican Pool, but it is a private swim club where you have to be a member (or guest of a member) to go. After you move in, consider getting on the wait list for the pool, as you'll want to have to option of going in future summers.
https://www.mohicanpool.org/membership/membership-information/
A great play to meet other families and young children is Wood Acres Park, which is just behind the elementary school. It's the largest piece of open space in the area, with ballfields and playgrounds. Worth checking out.
It will all be fine, and your son will find friends quickly. Good luck with the move and settling in!