Hi AWS, there’s a swimming pool, with small kids pool,
a small soft play centre down the Northgate, or a bigger one about 10 miles away at leadburn.
check this link http://www.wellybooters.co.uk/ for something a little different.
Directly opposite Glentress is the Sustrans old railway trail, it’s tarmac, and goes to Peebles, ideal for the kids to cycle on.