As has been said, zero evidence to support any detrimental harm to children weightlifting, and that's not for a lack of investigation. It has been investigated many times. Not just for injuries and such, but for the often quoted "height development". Scientists have investigated a potential relationship between lifting weights and height and have so far failed to find any relationship at all. Lifting weights as a child does not make you shorter.
Some of the most dangerous sports a child could possible take part in is football and rugby, by a long margin. And I'm not talking about total numbers of reported injuries, I'm talking rates of injuries. Weightlifting is way way down near the bottom of the table.
It may be odd to think about it over here, but in China and other Eastern European Countries, they all start lifting as children.
Now, there could be some other issues with overtraining and what these kids might be having to go through, but that's not specific to lifting.