Great article - really enjoyed it!
I actually have three girls (10, 6, & 4) and now that the 4 year-old is out of diapers, the whole family will be making their first trip together this summer/fall. My oldest has been backpacking since age 4. The middle one had to wait until 5 - she was just too dangerous :-). Now my youngest can go (she's relatively safe).
If it's just me and the older two, I will use a TarpTent Rainshadow 2, though we squeezed into a Squall 2 until I was able to get the Rainshadow this year. When all 5 of us go (including my wife), I plan to use the Rainshadow and the Squall. With two shelters, I can't wait for the inevitable fights about who gets to sleep where ;-).
Another great pack option for 10+ year-olds (though a bit expensive) is the Gossamer Gear Miniposa. I just bought one (size Small) for my oldest daughter and it fits quite well, even with significant growing room. The optional foam pad inserts are too wide (probably even to trim), but stuffing the shoulder straps with socks works great. My 6 year-old is just using a simple and cheap Coleman day-pack like backpack. My 4 year-old will likely just carry an old preschool backpack.
With five of us, though, I would be curious about any mealtime suggestions. I have both an Evernew 0.9L pot and an MSR TItan (0.85L) kettle with two alcohol stoves - that combo works great for three, but I don't know about five. Any ideas? Maybe a bigger (2L) pot for the main course (in place of one of the small ones) and perhaps a canister stove in place of one alcohol stove?