OK, info back from Bikers' Gear regarding $89 children's jackets:
S is 28" chest, 21.5" long and sleeve armpit to cuff 15.5"
M is 30" chest, 21" long and sleeve 16"
L is 32" chest, 21.5" long and sleeve 16.5"
XL is 34" chest, 22" long and sleeve 17"
2XL is 36" chest, 23" long and sleeve 18"
3XL is 38" chest, 24" long and sleeve 19"