The ACSM’s position (circa 2007), which hasn’t really changed since at least 1998:
“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.