Arnold is actually really short, I'm 5'7 and I'm taller then him, he just looks big in the movies.

Weight lifting can stunt your growth if you start extremely early and do the wrong exercises.

for example, no kid should be squatting weight untill he is 14, if a 9 year old seriously started hitting heavy weight, his bones would calcify and stop growing. That what happens when you lift weight, your bones get thicker, and if kids start to young, their growth plates will also close early.

the best thing for kids to do to stay strong is simple, just play outside. its so simple to go out and play soccer or football, or basketball and get strong and stay in shape, and its fun. weightlifting shouldn't be done untill a kid gets into highschool.