Lifting weights before puberty growth does not prevent children from growing to their full potential height. Bones grow from growth centers that are weakest part of bone, but strength training during growth does not damage these growth centers and children who lift weights in programs with experienced supervision do not suffer more injuries than adults. There used to be concern that growing large muscles would make people musclebound and interfere with coordination, but this does not happen. With increased strength comes increased speed and increased coordination in movements requiring strength.
Having large strong muscles makes you a better athlete. Muscle growth is limited by the size of the bones on which they attach, so the larger the bone, the stronger the muscle. Children who start to play tennis before they go into puberty have larger bones in the arm that holds the racquet. They also have larger bones in their tennis arm than those who start to play tennis later in life. The larger and stronger your muscles, the harder you can hit a tennis ball. The best time for future Olympians to start training is while their bones are still growing.