It's almost never a good idea for a kid to try to gain weight, especially by eating lots of junk food. Many people want to be thinner, so it can seem strange that some kids want to gain weight. But kids who are thin sometimes feel like they aren't the right size. And they might even get teased about it.

People come in different shapes and sizes. You might have friends the same age who weigh a lot more than you do. That doesn't mean that either of you is the wrong weight.

Why Do Some Kids Weigh Less?

Here are a few good reasons why some kids are thin or don't weigh as much as their friends:

• They're short. If you're not too tall, there's less of you — at least vertically. That equals fewer pounds when you step on the scale.
• They're small-framed, which is sometimes called "small-boned." It just means a person's body frame (their skeleton and muscles) might be smaller or thinner. One way to compare frames is to look at your wrist. A person with a smaller frame usually has a smaller wrist and might have trouble finding a watch that's not too big!
• They feel thin compared with friends who've gone through puberty. During puberty, it's normal for kids to grow a lot and gain weight, too. If one kid hasn't hit puberty and another has, the one who's still waiting for puberty is likely to be smaller and thinner.
• Their parents are short, small, or thin people. Your mom and dad pass along their genes to you — including the genes that help determine your height and body frame. If close family members are on the small or thin side, there's a good chance you will be too.

What About Getting Teased?

Being teased is one reason thin kids sometimes want to add pounds. It's never fun to be picked on. If this happens to you, be sure to tell a grown-up who can help. You might also rehearse what you will say back to someone who teases you. Don't insult anyone, but maybe say, "That's just the way I am. Everybody is different." Having friends who back you up can help you feel braver and less alone.

Health Advice for Thin Kids

Small kids especially want to know how to help their bodies grow and be strong. The best advice for all kids is to eat healthy foods, get plenty of exercise, and get enough sleep.

Trying to gain weight by eating a lot of extra calories is a bad idea. It can make you feel sick and is not healthy. So just listen to your appetite and eat only as much as your body tells you to. If you’re worried you’re too small, talk with your mom or dad. They can help figure out whether you should see your doctor.

Once in a while, a health problem can keep a kid from gaining weight. A kid who is not growing well or is losing weight may need to go to a specialist who can check things out, or to a registered dietitian who has lots of tips on how to eat well. But most of the time, thin kids don't need to see a doctor or go on a special diet.

Here's another surprise. All kids need to exercise, no matter their size. A lot of people use exercise to keep their weight under control or to lose weight. But there are many more reasons to stay active. Exercise builds strong bones and muscles, helps you stay healthy, gives you energy, and helps you feel good.