The 25 WSSM is about the equivilent to the 25-06 so recoil shouldn't be that bad. To say it was too strong for your 9 year old would depend on the child. It is not strong recoil but what other calibers has he shot with?
His age is not really the determining factor of his ability to accept recoil. I've been a competitive skeet shooter for years and have wanted to teach my brothers kids the sport. Most professional instructors (see Fred Missildine's book) will advise you not to start a child until he/she weighs 75 pounds. For skeet shooting that would be the min weight using a 20 ga autoloader to start. To much recoil to early develops bad habits...... the body will naturally avoid the sensation of pain. The kid may develop a flinch or a hesitation to pulling the trigger or something like that, all bad in shooting sports.
I'd use the same guide lines for rifles.
The goal of all hunters is a quick, humane kill where the animal drops in it's tracks and is dead within seconds. But in a pursuit that has as many variables as hunting, sometimes things don't quite go according to plan. However, game can be tracked and recovered with the right skills and with patience.
First of all, you need to wait the right amount of time after the shot before tracking a wounded animal. I've heard estimates of waiting 30 minutes for a hit in the vitals and 5-8 hours for a...