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 their size. 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. 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 develop. The best advice for them is the same as the health advice for all kids: Eat a healthy balance of foods, get plenty of activity (play time), and don't skimp on sleep. Trying to gain weight by stuffing yourself with 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 your size concerns you, 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. The kid usually goes 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. Kids who are thin need to exercise. A lot of people use exercise to keep their weight under control or to lose weight. But exercise serves many other purposes, too. Moving around helps you develop important skills and helps your body get stronger. And unless a kid has gone through puberty, weightlifting won't build bigger muscles. It also could hurt bones, joints, and muscles if it's not done correctly. You want to help your body, not hurt it. Treat it right and you'll grow and develop just the way you should. Back to Articles Related Articles Be a Fit Kid A lot of people talk about fit kids, but how do you become one? Here are five rules to live by, if you want to eat right, be active, and keep a healthy weight. Read More Feeling Too Tall or Too Short How do you like your height? Check out this article if you feel too tall or too short. Read More How Can I Feel Better About My Body? It's normal to wish you could change something about your body. Find out more about these feelings in this article for kids. Read More Learning About Calories You've probably heard about calories. Are they good or bad for you? Find out in this article for kids. Read More Go, Slow, and Whoa! A Kid's Guide to Eating Right Want to eat healthier? It's easy when you learn the difference between Go, Slow, and Whoa foods! Read More MyPlate Food Guide MyPlate is designed to make it easier to understand healthy eating. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.