Are your kids overweight or just about right? If you think they’re about right, you’re like most parents in the United States, according to research.

But a lot of parents are wrong, and you might be, too. About 17 percent of kids and adolescents ages 2 to 19 are obese, up from 5 percent in 1974, according to data from the Centers for Disease Control and Prevention (CDC).

That increase is a big problem because childhood obesity is a reliable predictor of adult obesity. Obesity in adulthood is a risk factor for heart disease, Type 2 diabetes and other chronic diseases, making it a leading cause of preventable death in the U.S. No parent wants that for his or her children, but you can’t fix a problem you don’t know exists, which is a common problem for parents of obese kids.

First you have to find out whether your kid has a weight problem by seeing a pediatrician. Then, if necessary, you can come up with a plan for a healthy, active lifestyle for your family that includes a positive, supportive environment. Here’s where to begin— even if you’re not quite sure there’s a problem.

READ MORE: State by State: How Much Does Obesity Cost You?

Discovering— and admitting— the problem

According to a large national study published in the journal Childhood Obesity, 78 percent of parents with an obese child— almost 4 in 5— perceive him or her as “about the right weight.” That’s up from 71 percent in 1994, according to the study.

Parents’ perception of their children’s weight is important because it influences whether they foster healthy behaviors at home, says one of the study’s authors, Dr. Jian Zhang of Georgia Southern University’s school of public health.

“Our socially accepted standards for ‘normal weight’ may be shifting upwards, presenting a vast challenge to childhood obesity prevention,” he says.

Even if you think your children look about right, it’s best to know for sure by taking them to a pediatrician. A pediatrician can identify temporary changes or an underlying disorder that affects children’s growth or weight.

If your child is deemed obese, stay calm, says Dr. Christina Economos, co-founder of ChildhoodObesity180 at Tufts University, a group of researchers and professionals who collaborate to combat childhood obesity.

“It’s a problem, but don’t panic. As a parent, there’s a lot you can do,” she says.

READ MORE: Eating Healthy on a Budget

First steps

When you discuss your child’s weight, focus on health. If you need to break it to your child yourself, let him know the doctor says he is gaining weight too quickly, and the whole family is going to make healthier decisions. Then ask him to think of some new activities he’d like to try. Avoiding ridicule and punishment will create an atmosphere of support and increase the chances that your child will adopt healthier behaviors both in and outside of the home.

Even if you couldn’t tell your child was overweight, he or she may have been teased or even bullied at school already.

“Kids are pretty delicate, and that’s really heartbreaking stuff, so adults should be positive and supportive,” Economos says.

You’ll also want to make a plan of action with your child’s pediatrician, but first you both need some information, including how overweight your child is and how much he or she should be eating.

Be prepared to tell the doctor about your child’s eating and activity habits, including any foods he or she won’t eat. If you have a picky kid who won’t eat vegetables, for example, your doctor may connect you with a dietitian who can teach you ways to sneak more veggies into your family’s dinners.

READ MORE: Easy Ways to Sneak in More Vegetables

By the end of the visit, you should know what steps to take next, including how to make healthier meals and find fun activities to get your kid moving.

Enlisting your team

Even if you’re a single parent, you don’t have to be the only adult helping your child lose weight; it’s best to include everyone in your home in your new healthy behaviors, including children who are at a healthy weight. Extended family members, teachers, coaches and religious leaders in your community can all play a part, too.

“With this sort of team approach, the child can navigate healthy behaviors in lots of different environments” rather than just at home, Economos says.

In addition to telling close contacts about your child’s new diet and encouraging physical activity, discuss with those people why and how they should help facilitate your positive atmosphere. Tell them it’s not about taking away junk food or TV time— it’s about nourishing and fueling the body properly, and finding fun ways to get active.

“In the end, it may help a lot of children,” Economos says. For example, “if a coach puts out a rule that it’s water only on the field [instead of sugary sports drinks], that benefits the whole team.”

READ MORE: The Most Dangerous Sports for Kids

Keep expectations in check

Finding healthy recipes online is great, but don’t use advice from non-professional resources. Whatever you do, steer clear of fad diets and blogs offering nutritional rules for children.

“Children who are growing need adequate nutrition, so you really need to follow an evidence-based approach as outlined by real clinicians,” Economos says.

And even though this is a big change in your family’s lives, it doesn’t have to be all-consuming. Keep changes small and manageable by integrating them into your daily life, and you’ll be set up for success.