H. U.,
Been to Glacier 1 weekend and it was fogged in and raining for most of it. Avalanche Lake was an easy hike to an impressive lake basin.
Been through Banff/Jasper twice. Lake Louise area is very senic, but also very crowded and touristy. Columbia Icefield is worthwhile but can be crowded as well. There's a salt lick off the side of the road between the town of Jasper and the Icefields that usually have Mountain Goats there and it would be easy access for the kids. Mount Robson is very impressive and is just west of Jasper. Also a lot less crowded by the time you get that far north. All those parks are very senic, and crowds or not, it will be a trip the youngsters remember for the rest of their lives. Have fun!