I don't know much about fishing the Upper/Lower lakes, but there are lots here that can speak to that.
You can head out to Elbow Lake, which is a 20-30 minute drive from your campground, and then a 1.2km hike to the lake. That should be doable with kids. There's lots of little brookies there, and you can keep up to 5 of them if you want to eat them. The lake is overpopulated with brookies, so you'd do the lake some good by taking a few out. Fishing is great from shore.
Anything small (size 18 Adams, parachute Adams, mosquitoes, griffiths gnats, etc.) work well with 6x tippet, and for kids, you can tie on a bobber, then 2 feet of tippet and a small nymph. Cast out and reel in, and you should get some tugs.
Hope that helps.