i have heard that gym workouts stops our height growth .. is it true?
Physical activity (regardless of its form) should not stunt growth in anyway. What should be more of a concern is getting kids to specialize in specific sports way too early in their development (as opposed to having kids develop general fitness and gross motor movements). Early specialization leads to imbalanced physical development and increases the risk of injuries.
Should a child be exercising in a gym, they need to make sure that they receive a general fitness program that covers all aspect of physical fitness, or at least engage in a variety of activities to ensure that all aspect of physical fitness are being met.