It is generally easier for a child to lose weight than an adult for a variety of reasons. The biggest reason being that a child is still growing, still developing and hormones are coursing through their body as they get older, making it easier for them to get rid of excess weight.
After this, there is a growing percentage of overweight or obese children, especially in North America. The good news is, armed with the proper knowledge children can lose weight & actually enjoy doing it!
The first step for a child to lose weight is to adjust their eating habits. In general children do not eat well, especially if their parents set poor examples. Things like fast food, fruit juices (except 100% fruit juices), sports drinks / energy drinks & high sugar foods like cookies, cake, etc. should be removed from their meals.
Once in a while it's OK to have unhealthy food, but most of the time they need to be eating food that is actually good for them in order to lose weight.
The second step is to get up and exercise. Children and adults need about 30-60 minutes of exercise a day in order to get & stay in good shape. This does not have to be all at once, but it is important to make sure that they are getting daily exercise.
Video games and watching TV play a large role in the high percentage of overweight children. Rather than going outside and playing with their friends, kids are staying home sitting in front of the TV or the computer like zombies, burning few calories and often eating mindlessly while they are playing / watching.
This means in order for a kid to lose weight, they need to cut down on TV watching & video game playing and do things like playing sports, swimming, bicycling, even doing chores to burn off calories.
You should not have to force your child to go out and exercise. Just find something they enjoy doing. It could be jump rope, throwing a football, shooting hoops, playing street hockey, building boats, having snowball fights or water fights, the list is endless. There are so many ways to get exercise, you do not have to limit it to playing a team sport or going out for a run.
Lastly, one of the most essential components of kids losing weight is having an example in their parents. Many parents do not set good examples for their kids, and unfortunately kids do what their parents do.
If your child is overweight & you want them to lose weight, then you need to set an example and clean up your act. Eat proper food, exercise regularly, and be supportive of them in their efforts to lose weight.