I know that's how it's supposed to work, but i noticed myself that it doesn't 
. The adjustments are meant for people in the same size category generally speaking, and just growing up, i grew out of the pack i used when i was a kid (bought when i was 14 i think, terrible for use by me when i was 17-18 something. (Though i'll admit that the adjustable back system did help me use the pack a bit longer.) It was a cheaper pack though, and it was still good when i stopped using it and gave it to a friend of my dad's for his kid. That's why i'd suggest not looking for a durable long term (generally expensive) pack for kids, but go with a cheaper pack. Buy a good pack when they grow up and you're sure they'll be good with the pack for a long time .
(And then went the cheap aldi pack route, Sabre45 with side packs, Osprey Stratos 36 and now looking for a lighter 60L pack but without any urgency.)
. The adjustments are meant for people in the same size category generally speaking, and just growing up, i grew out of the pack i used when i was a kid (bought when i was 14 i think, terrible for use by me when i was 17-18 something. (Though i'll admit that the adjustable back system did help me use the pack a bit longer.) It was a cheaper pack though, and it was still good when i stopped using it and gave it to a friend of my dad's for his kid. That's why i'd suggest not looking for a durable long term (generally expensive) pack for kids, but go with a cheaper pack. Buy a good pack when they grow up and you're sure they'll be good with the pack for a long time .(And then went the cheap aldi pack route, Sabre45 with side packs, Osprey Stratos 36 and now looking for a lighter 60L pack but without any urgency.)