Knapsack/Backpack Strap Adjusters!

[bagheera]

All right, I'm making a modified Monster Bag, for a little 2-3 year old girl. I'm making it as a knapsack. I finally decided to do the straps with nylon webbing (I'm pretty sure that's the right term, similar to the stuff they make dog leashes with?)...

I have two strap adjusters, kind of like the ones on this backpack. I'm wondering, are there any step-by-step "for dummies" instructions for threading and properly attaching backpack straps, so that as she grows, she will still fit the backpack?

Thanks a billion for your help!