Can i ask both coaches a question?

My boys (10-12 years old) play sports competitively (ice hockey, swimming and golf). Do you think it is too early for them to have endurance and weight training? They are tall and skinny, very strong, but lack core strength and endurance. Their sports coaches think it is too early to do weight training (they start to incoporate some at 13-14, and a bit more at 15-16). I am thinking to get them a licensed coach in  my gym (I have membership in a top facility) to do weight training once a week, but not sure if this will impede their growth (height wise, since they just start to grow). Any suggestions? Thanks!

I read all your article, bronzegoat! I love what you write and your big warm smiles! BTW my boys are half German but we live in the US.

Coach 1960s I read your posts too. Very helpful!