I like SD's suggestion of entering at Beaverhouse, and basecamping on Quetico or Cirrus. You can easily spend time on both lakes without moving camp daily. By spending your days, fishing, exploring, berry picking, etc., you are more likely to acheive the goal of giving the kids a good time. This is important if you want them to look forward to the next trip. Most kids that age have an allergic reaction to anything percieved as work (such as moving camp). Be sure to involve them in camp chores. Let them gather firewood for the evening bonfire. Let them help with cooking & dishes, etc. This teaches them the importance of doing their fair share. Let them carry what they can handle on portages (using appropriate sized packs). You get the idea.

You could do something of a loop by entering on Quetico, stay there a couple of nights, then move to western Cirrus, for a couple of nights, and back to Beaverhouse. Or the reverse.