Your pediatrician can tell you if your son is growing normally by routine height and weight measurements plotted on a growth chart. Hard training will not impede his growth, as long as he is eating adequately. If he seems overly fatigued and lethargic, he may be eating too little. An easy way to boost calorie-balance is by replacing water intake with more milk and juice. This will balance the number of calories he is burning in the play activity. Active children may need as many calories as their parents, if not more. For example, the average 6-year-old needs 1360 calories per day. More, if they play sports. With sports, their calorie requirement can increase further.
Nutrient Requirements for Indians (RDA & EAR), ICMR-NIN, 2020