Without reduced loads it's a big jump for a kid. I watched someone let a 10-11 yr old shoot a 270 after only ever shooting a 22. The kid wasn't unusually sensitive, but it was a full power Corelokt and definitely did his best to fight back a tear or two. I think a big issue with smaller kids is that they can't hold a full sized stock in tight, so rather than a push, they get a hard jolt.
10-11 year olds also don't have as much muscle mass on their shoulders--which is a big reason more recoil can actually hurt, not just jolt them back.
MD hit the nail on the head regarding muscle mass. Spent 16 days in the hospital in March. Loss 30 pounds of muscle mass including shoulders / upper body. Checking zero on my favorite .243 and .270 last week from the bench. No issues with the . 243. However, for the first time ever, the .270 shooting factory Nosler 130 NAB's, "hurt". Sore bones for a several days.
Similar situation to the OP about 10 years ago with the oldest grand daughter. Picked up a Marlin XL7 in .270 for a reasonable price. Put it in a Boyd's laminated stock with LimbSaver recoil pad, and loaded up a couple boxes of 110 grain NAB's. She had zero issues with recoil, and killed three KY White Tails over the following three years without issue.
