Flyfrod,
I'll send a question back your way. Do you reload?
Back to that in a minute. You may need to buy a youth rifle to get something that fits properly unless the 9 year old is big for his age.
Now, if you reload, an easy answer to your situation is reduced loads.
If you have hunted and taken game animals, how many times have you felt the recoil or heard the blast of your shot?
I'd guess seldom if ever.
The point to that being if the rifle fits correctly so the shooter doesn't get a scope bite, the recoil of a full power hunting load fired at game is a non issue if the rifle is of reasonable size/recoil.
Soooooooooo, in my case, I have loaded reduced practice loads for family members and friends who were shooting 270s.
Load the lightest bullet you can find, load a proper powder which provides a safe reduced load/velocity and head for the range.
Use small targets in close - dime or quarter size, and the relationship with a larger target/critter at normal hunting ranges will be close to the same.
Make it reduced loads with the targets in close and be sure you take enough ammo as young people can burn up a lot when they are having fun.
Another plus is, the reduced loads cause less heat build up in the barrel, so there is more shooting and less waiting for the barrel to cool.
Also, you do the pre season sight in from the bench, with the normal power hunting loads.
Crusty Deary Ol'Coot