so the question becomes are you training for athletics or are you training him just to have him become stronger, more confident and gain muscle?

because there is small differences in how you should train him for each

1) ignore anyone that says that is too young or mentions growth plates, they are ignorant as frick on the subject and should immediately be written off

2) no matter what he is training for, it should be a program based around compounds lift and bar speed. When training kids that age, have to understand more gains are going to be neuro and not muscular. This is why a VBT device can make a huge difference in intent and setting PRs. allows them to set PRs without it being strictly weight driven.

3) he has to eat, lots of protein

there have been couple good post above and the linked posted has some programming i have written for kids in the past

you want to focus on compound lifts, if in athletics that would be box squat over back squat and add jumps, deadlifts would be sumo instead of conventional, paused bench over bench and lots of med ball throws

both ways add unilateral work and its very important to get enough mobility to do a crossak squat properly and maintain that ability. want the stability to be able to do reverse lunges and full range of motion in knee over toes squats

for mobility work, slow crawls like bear, reverse bear, duck walks, crab walks, alligator walks etc are your best friend.

make sure they can do calisthenic work. very important a kid doesnt go into high school without being able to do basics like chinups, pushups squats.

if you want more specifics just let us know

congrats on being a good dad though. Physical literacy is very important and the decision you have made will help him in all aspects of his life. its proven to help with grades, confidence, body image, on top of all the other health benefits.