Take walks with your child after meals
Take up sports which the whole family can do
Teach kids how to swim and ride bikes at an early age
Don't encourage kids to watch TV and limit computer time

Here are some tips for parents whose child are overweight:-
1.Don't forbid any foods, simply limit them. If your kids want to go to McDonalds occasionally, fine. Just don't make it a regular occurrence.
2.Don't force your child to eat if they are not hungry. Children's appetite vary and often during a "growing spurt" they lose their appetite. Don't worry when this happens, as soon as their growing spurt is over you will find they eat extra to make up.
3.Encourage them to snack on healthy carbs like whole grain cereals with low-fat milk, whole grain bread with a light spread of peanut butter and jelly, or fruit spread or fruit breads.
4.Encourage them to eat fresh fruit regularly(keep it on our dining table or on your fridge).
5. Make salads more interesting by adding fruits like grapes, sections of mandarin orange, chunks of pineapple, sliced peaches.

Make him more interested in playing outdoor games like basketball and tennis. The exercise will do him good. Restricting food by talking to him is a must.

A child's mind is blank. They just imitate what they see on adults. So your aunt can influence her son to eat vegetables by eating vegetables. That could be seen on her also. When her child sees that she eats vegetables, it is most likely that her son will eat it too. Also, she must always prepare vegetables as part of the menu. At first, the child might not like it but as he gets familiarized with the veggies, he will get used to it.