trying to figure out what we can do in 2 days...
can you give us more detail? I take it you are from Calgary - what do you want to do in Kootenay Park? Do you have plans re where you are going to stay? camping/hotel? I'm certainly not the best person to advise on what to do in the park - I'm the type that tends to bomb through the park trying to get to Calgary (Ikea, Chapters, the Bay, A&B Sound when they were still around, Toys R Us etc etc) as quickly as possible, so I don't really "know" the park at all, but I do know that KNP is often seen as the "quietest" of the Rockies Nat'l parks, so I'm kind of curious as to why you are choosing KNP in the first place?
Have you looked at the Kootenay National Park website? There seem to be activities focussed on children. I'm just not sure if they are suitable for the age group of yours -
Perhaps contact them and ask.