Child obesity starts with what children eat. Any child who is obese could have glandular problems, but that only makes the work much harder. Calories and fat come from somewhere and that is in the food. Diets and diet foods don't usually work. Diet foods tend to make you hungrier rather than energize your body.
Instead, go back to the basics. Give your child a little reign on the decisions about food. Go with her to the grocery store and check out the fruits and vegetables. Does she prefer apples to oranges? There is no harm in letting them choose the fruits they like best. Stick with juice, milk or water. Would they like something sweet? A bowl of juicy fruit gives them the vitamins and minerals they need and satisfies a sweet tooth. Serving baked goods, ice cream or sweet treats on a rare occasion is fine, but keep it controlled. In other words, this should not be a nightly event. Keep food interesting and varied and your child will learn how to pick a variety of healthy foods and eat properly as a general goal every day..
Child obesity is not something that goes away overnight. Kids need to eat properly and to exercise. Find a hobby your child likes, perhaps basketball or swimming, or tennis. Help them to become healthy and yet still enjoy it as they are exercising. You and your child will both be healthier and happier.