Welcome to Westwood. I'm not that knowledgeable about programs for children as our daughter is only 16 months old and still in day care, but here are some ideas:
The town has a some programs through the
recreation department. The town pool is open for swimming (for a fee), but if you have access to Lifetime that will be a better choice. Considering where you are in Westwood (which is pretty far removed from the bulk of the town, same as me), the towns of Canton and Norwood will be just as close if not closer. I think Canton offers non-residents access to programs, so that might be worth looking into if you don't like the Westwood options; I'm not sure about Norwood.
The
Hale Reservation runs camps through the summer. You are probably too late for this year. They also have a membership beach.
If you're interested in ice sports, the
Boch Ice Center is right across Rt. 128 in Dedham. They offer programs for kids, although I'm not sure if it's after school, but with in-laws from Minnesota I have been made aware that these programs are available.
Let me know if you find some good options. I will be looking in a few years!