QMy brother and his family have always been supportive and loving to me through my many years of travels and tribulations, and I have a good relationship with them.
They are great people and are really important to me.

I have also been blessed with a special relationship with my niece, who is 9. As a young child, she was always healthy and slim, but lately I have noticed that she has gained a lot of weight and has stretch marks on her tummy. Her eating habits also have changed, and she now literally shoves food into her mouth and stuffs herself with unhealthy snacks.

I watched my mother slowly kill herself because her obesity caused so many health issues. My brother, who has always struggled with his weight, simply says that he inherited the problem. I disagree. I am not a supermodel, but I’ve found the discipline to maintain a healthy athletic figure. This, to me, is living proof that our family doesn’t have to be fat.

When my brother and his wife let my niece eat the way she does, however, it feels like borderline child abuse to me. Can I address this concern with them? Should aunts and uncles be quiet when they see parents overfeed their children? Or am I overreacting?

AMaybe you are overreacting, but with good reason. You saw obesity take away your mother’s health and then her life. Now you’re watching your beloved brother accept obesity, too, and even let his daughter get near that slippery slope. Because this situation has probably made you angrier than you realize, it’s probably better to be quiet than to say something that could hurt the feelings of the people you love.

You also should know that weight problems do run in families, though they may not affect the whole clan, and that many girls and boys pork up a bit between 9 and 12, but they usually get taller when they’re around 14 or 15 and start looking slim again.

You don’t want your niece to become a chubby teenager, however, because she would probably think of herself as chubby for the rest of her life, no matter what she weighed, and you definitely don’t want her to get fat in her teens, because a fat teenager is 10 times as likely to become a fat adult.

That won’t happen to your niece if she gets plenty of exercise and follows the basic rules of good nutrition.

Like every child, she needs a half-hour of exercise for every hour she spends in front of a TV or a computer and even more exercise if her school has cut phys ed out of the curriculum, as most of our schools have done. She also needs a doting auntie to invite her to go on bike hikes or to swim at an indoor pool or to try karate at your gym or to lift weights in your living room. There is sure to be a sport or an exercise that is right for even the most sedentary child.

There are limits to what exercise alone can do, however.

Your niece also needs to know that children gain more weight if they eat while they watch TV, if they sit in front of a TV or a computer for four hours or more every day, and if they eat a lot of processed foods.

Although you don’t want your niece to obsess over calories, have her write down everything she eats for one week and then count the calories for her, so she can see how quickly they add up. She’ll then understand you better when you explain that she will gain a pound if she eats 3,500 more calories than she needs in a week but lose a pound if she eats 3,500 fewer calories.

She also must learn that it’s healthier to drink water than to drink a soda; that it’s better to eat fruit than to drink fruit juice; that she needs only two or three glasses of milk a day, not four or five; that she needs three meals and two high-protein snacks every day; that breakfast is her most important meal; and that oatmeal — or grits with an egg on the side — will stick to her ribs much longer than a sugary cereal.

Although your brother and his wife probably aren’t ready for you to give them a lecture on nutrition, you can give them a subscription to Nutrition Action (www.cspinet.org). This health newsletter is published by the Center for Science in the Public Interest, which has probably done more to improve food in America than any other organization.

Questions? Send them to advice@margueritekelly.com.

More online

3Almanac archive ­Read past columns at washingtonpost.com/advice.

3Next week Marguerite addresses how much is too much electronics for children.

3Kid-friendly events Find ways to entertain your children in the area at goingoutguide.com/kids.