Seymour,
my wife and I spent a lot of time in that area with our very young kids
( youngest kid we took was 4 mo. old for 13 days ) when we were first introducing them to Quetico. We actually went the other way and headed west from the ranger station and just stayed on Beaverhouse. 1 portage in and 1 portage out. Keep it simple with young ones. There are some nice spots on the far west end of the lake that you can base camp at and there are a couple of sand beaches on that end of the lake as well. You can paddle down to the outlet of the Quetico river and explore that area. Fishing is very good on that end of the lake too. All 4 species. You are far enough away from the ranger station that the planes are not obnoxious and they don't come in every day. Not many people go to that end of the lake so it actually feels more remote that it really is. And if there is a problem, you are not that far from the ranger or your car.
Start them young and they will love it for life.  Good Luck.
Gene M