From a recent meta-analysis:
“In conclusion, there is no evidence that currently available interventions are able to increase physical activity among overweight or obese children. This questions the contribution of physical activity to the treatment of overweight and obesity in children in the studied interventions and calls for other treatment strategies.”
Source: Effectiveness of interventions on physical activity in overweight or obese children: a systematic review and meta-analysis including studies with o… – PubMed – NCBI
For weight loss in overweight and obese children, you have to focus on diet modification. Same as adults.