Lava Hot Springs is about 20-30 minutes away from Pocatello. This is a fun water park, especially for the kiddos. Multiple slides, dive boards, and outdoor and indoor pool/hot tub are offered. There are lots of fun things to do in Lava as well. You can float the "river" (it's pretty small, but people love to do it), explore the fun shops, eat some good food, and they have natural hot springs!
Something fun for the kiddos in town.
If you don't want to drive to Lava for the pool, there's one in town! It has a lazy river, deep pool for the adults, and a really fun kiddy pool.