if you're looking at stopping half way then that would probably be around armstrong... not much to see or do there. i'd recommend heading to either vernon or kelowna
i'm not sure which places have pools. i know that the fairfield in kelowna must have something - they've got one of those water slides that comes out of the top side of the building and then back in at the bottom. the fairfield is right around the hwy 97/hwy 33 intersection.
stuff do to along the way.... i'm not sure for little kids, but i always enjoy the scenery. there are lots of places to pull over and walk around for a few minutes. when passing thru kelowna your more than welcome to stop by my place and 'take in the games room'
there is an aquarium in vancouver. i haven't been there since high school (i'm sure it's changed a bunch in over 20 years). my wife's school always does a grade 7 field trip to the aquarium and i know every year when she returns from the trip she has tons of stories of how much the kids enjoyed it
there is lots to see and do in vancouver... although i find my trips usually consist of 3 things....
1 - visit relatives
2 - follow my wife around for endless hours at the malls
3 - watch the flames beat the canucks at gm place (the flames have an awesome record when i get to games!)