It is not lifting weights early in life. The chinese, poles, bulgarians, russians, etcm have had their weightlifters lifting at young ages often as young as 8 yrs old, albeit they are typically more patient about it and very methodical and progressive. They do not have these injuries, if anything, they have stronger than average bones from lifting. The key is not to lift too heavy too young.
More likely would be stress fractures caused by excessive and too high volume of running that then turn into real breaks later. This is common in Navy SEAL training where a trainee does not train enough before BUDS and has not accumulated enough volume then they hit training, the volume is ramped up a little quicker and they end up running down the beach and Bam! the leg breaks, even at the femur.