Your weight has been important since the moment you were born. Maybe you even know what your birth weight was. Most newborns weigh between 6 and 9 pounds, but some may weigh more and some less.

But very quickly, a baby gains weight and everyone is glad about that because it means the child is growing bigger and stronger.

As you get older, your weight is still important. It's something your parents and doctor will probably keep an eye on. When you go for a checkup, the doctor often will record your height and weight and compare it with what it was the last time you came in. The doctor wants to check that you are a healthy weight because weighing too much — or too little — can be a problem.

But these days, being overweight is more common than being underweight. More kids and teenagers have weight problems than ever before.