Tigerchik is talking about damaging the growth plate before the bone has had a chance to fully develop. I believe the primary issue with a growth plate fracture is the potential that the affected limb will not fully grow/develop. In youth runners we see inflamed growth plates a lot in the ankles. Usually rest works but her point is valid and should be considered especially where the training the OP is contemplating is not the primary focus. In other words, I’d be concerned about over-doing the hill/speed work since the kids he’s working with are not fully developed nor focused on running as their primary activity.
No mention of the dangers of strength training to growth plates. But it does recommend certain types of strength training to protect against growth plate inflammation and injury.
What you are suggesting makes sense, but I doubt that you are going to be able to do much to improve their speed at little league baseball practice. As for the kid swinging in slow motion, assuming that you have made sure that his bat is light enough and that he is chocking up on it, then tell him to swing at the ball like he’s angry at it. Another father that played minor league ball suggested that to us, and it helped our son’s hitting out.
You can probably get them to run faster and teach them how to run bases better at the same time if you make it into a game, like some sort of relay race. But, don’t try to do too much. They are kids, and you want to make it fun so they enjoy practice.
“Contrary to the traditional belief that strength training is dangerous for children or that it could lead to bone plate disturbances, the American College of Sports Medicine (ACSM) contends that strength training can be a safe and effective activity for this age group, provided that the programs properly designed and competently supervised.”
you’ll find the following caution at the very bottom, which may be the source of confusion, but it they apply it only to ‘maximal weights’
“Strength training with maximal weights is not recommended because of the potential for possible injuries related to the long bones, growth plates, and back.”
But read the research, Malina did a good review in 2006, and there are a few studies on the efficacy of 1RM testing and training in kids… you’ll find the idea of strength training causing growth plate damage is a common myth, but not supported by the research. Those types of injuries are almost entirely caused by acute impact and/or shear forces - skateboards, falling out of trees, snowboarding, etc., not weight training.