The teen years are inherently tough. The addition of a weight problem to the physical and emotional changes already in store for your child with puberty makes these years that much tougher. On average, puberty starts between ages eight to thirteen in girls and ages nine to fourteen in boys. When girls reach puberty, they gain body fat in the breasts and hips, while boys develop more muscle mass. Both result in weight gain, and this transformation can make an already overweight child feel even more self-conscious. Make sure your child is aware that the changes to her body are completely normal and that everyone goes through them at some point in their lives.

Changes in hormone levels can also cause mood swings and emotional outbursts in your child, which can affect both her drive and attitude towards exercise and healthy behaviors. Usually these temporary mood swings don't stick around long enough to be a major detriment to your child's fitness program. But do be aware of the signs and symptoms of depression in case it's more than just moodiness.

Growth Spurts

Once a child reaches the end of his growth spurt of puberty, he will have reached his full adult height, with no further opportunity for “growing into” his weight. This occurs slightly later in boys than in girls, who usually reach adult height about two years after their first period. Just how tall your child gets is determined largely by the height of his parents; there are several formulas to predict adult height, but none is completely foolproof.

Two simple ways to get an idea of your child's ultimate height are the two-years-times-two method and the genetic potential formula. The two-years-times-two method is just that — take your child's height at two years old and double it. To compute your child's predicted height using genetic potential, add Mom's and Dad's heights together, divide by two, and then subtract 2.5 inches for girls or add 2.5 inches for boys.