regarding general training for kids, I’m gonna just copy/paste my response to another thread from a while back, as these remain my opinions. It’s long.
This is a very interesting topic.
The Soviets did numerous studies, and had State wide data collection on their athletic youths. They tended to introduce weight training to kids who were 11-12 years old. Any younger than that, and all their training was games, tumbling (rolls, gymnastic stuff), jumping, sports, and calisthenics.
Most recommendations are to limit heavy weight training to people older than 15.
According to Thomas Kurz and studies by Sulmitsev/Krumm…
Youths 11-12 years old can use weights up to 30% of their bodyweight
Youths 13-14 can use weights up to 50% of their bw.
Youths 15-16 can use weights up to 100% of their bodyweight.
Regardless of age, maximal strength exercises and great intensity lifts were not allowed until the development of the long bones had been completed ~= 17 years of age.
The Soviets’ State wide programs and studies also came to the conclusion that children 11 year or under should only use weights that they could do 13-15 reps with. And especially that children should develop their power and strength by running, jumping, throwing, tumbling, and NOT heavy external weights. This was done for a variety of reasons, but the primary one was probably for increased “motor learning”–eg. the more diverse movements you ingrain into a child while very young, the better they master new movements and their chosen sport later in life. In other words it increases their movement “vocabulary” if you will.
Also, it’s worth noting that Kurz states in his book (with a number of different studies by the Soviets and other countries cited that I don’t want to reference now because I’m lazy) that in children the different athletic qualities are all tightly related.
Simply, this means that making a young child agile will make him stronger. Or that making him more coordinated will make him stronger. It’s like Zen in reverse–early on, any kind of training affects all attributes of strength speed and agility, but the more the child ages into adulthood the more independent these qualities become. You train agility, you gain endurance and strength as well. You train endurance, you actually get stronger.
An adult does not get stronger by becoming more agile. If an adult trains endurance he will get weaker, not stronger. He has to train agility to become agile. He has to be specific to the athletic quality he wants to improve, whereas a young child can do anything he wants and improve on everything at the same time.
So short answer is he can train with weights before puberty with no problem, but the best strength training for kids is that he should get involved in as many different physical activities as possible for as long as possible. Get his movement “vocabulary” as diverse as possible. Make him run and jump and tumble and throw. Use primarily bodyweight exercises like push-ups, etc. Use light weight training as a supplement to all these activities, not the mainstay.
Hope that made sense.