The discussion about childhood obesity tends to center around the diseases caused by the extra weight. Children getting "adult-onset" diabetes and having other illnesses that many people correlate with middle-age. The topic that doesn't seem to be broached is the number of fat cells and how they will work on a person's weight for the rest of their life.
Not every person has the same number of fat cells in their body. Researchers believe that obese children have up to five times the number of fat cells as other children. The more fat cells a person has, the less leptin the body produces. Leptin boosts metabolism and signals satiety. That means that obese children will have to fight five times as hard as adults to maintain a healthy weight. Possibly harder.
The number of fat cells that you have when you reach adulthood will not change. The size of those cells will change if you gain weight, or lose weight, but the quantity will remain the same. Even if you gain or lose hundreds of pounds, you will not change that number, just the volume. The number can be changed surgically via liposuction, skin removal, breast reduction or similar procedures. This can lead to a problem if there is weight gain after the surgeries. Because the fat cells are no longer distributed throughout the body naturally, the weight gain can appear lopsided and in "odd" locations. No one wants to be shaped like an actual fat cell. (a stuffed one is below.)
This may be difficult news to read for people who were overweight kids. It's sad and unfair that it's going to take more effort for you to lose weight and keep it off than for someone who was thin for their entire childhood. That does not mean it can't be done. With dedication to a healthy lifestyle, you CAN maintain a healthy weight. I do hope this information makes it out to parents to stop brushing off heavy children's extra weight with a, "They'll outgrow it" mentality.