More than 29 million Americans have diabetes — yet an estimated eight million don’t know they have it. And the undiagnosed include a surprising number of children.

“An alarming number of kids under 18 have diabetes or prediabetes. But a lot of pediatricians aren’t checking for it,” said Dr. Sheri Colberg, a professor of Exercise Science at Old Dominion University in Virginia.

Colberg said it’s critically important that parents help their offspring avoid or manage diabetes—which can be especially harmful to young people if it’s not controlled because they suffer for the rest of their lives.

“When you get diabetes early, you have many more years to be exposed to its consequences,” said Colberg, author of “Diabetes-Free Kids.”

According to the Centers for Disease Control, Type 1 diabetes—which occurs when the body doesn’t make enough insulin—is diagnosed in more than 18,000 young people each year. Type 2 diabetes, which is diagnosed in more than 5,000 young people annually, occurs when the body can’t use insulin properly.

The increased onset of Type 2 diabetes in children has a lot to do with lifestyle factors, according to Jill Weisenberger, a diabetes expert and educator.

“We’re seeing more kids with Type 2 diabetes largely because of increasing rates of overweight and obesity. The problem is worse when the child isn’t physically active and eats a poor diet,” said Weisenberger, author of “Diabetes Weight Loss. “Obviously, parents have a have a huge influence over whether their kids eat a quality diet high in fruits, vegetables and whole grains or a poor one that’s heavy in such “white carbs” as rice, pasta and sugary foods.

“Many parents who’d never dream of putting a bowl of sugar in front of their kids let them have lots of soda. What they don’t realize is that a typical can of soda contains up to 17 tablespoons of sugar,” Colberg said.

Here are a few pointers:

• Realize the importance of catching diabetes early.

The symptoms of Type 1 diabetes are typically sudden and severe, so they’re hard to brush aside. But that’s not the case with Type 2.

“It’s possible to have Type 2 for many years before it’s diagnosed. Finding your child’s Type 2 diabetes and treating it immediately with lifestyle changes and perhaps medications is the best way to set him or her up for a healthy future,” Weisenberger said.

Make sure your children’s doctors are watching for diabetes—especially if you have a family history.

“If your child shows signs of diabetes—fatigue, increased thirst, increased urination or blurry vision—let the pediatrician know,” she said.

• Encourage your kids to exercise.

It’s no secret that many kids are living more sedentary lifestyles than their parents and grandparents did. In most homes there’s lots more “screen time” involving both TV and video games.

Because exercise plays a vital role in diabetes prevention, Colberg urges parents to build movement into their kids’ routines. One way to do this is to make exercise gear easily accessible in your family room.

“Near your TV, place a mini-trampoline, a hula hoop or balloons they can play with even while they’re watching their favorite shows,” she said.

Also, Colberg recommends that parents create tangible incentives for regular exercise. For instance, make it a condition of your kids’ allowances to walk the family dog daily.

• Try to make sure your kids to eat healthy.

Even more than exercise, diet has an impact on the incidence of diabetes. Colberg advises parents to take a multi-faceted approach to diet that begins with quality family meals at home rather than at fast food restaurants.

One approach is to fortify popular entrees with healthy ingredients. For instance, use whole wheat pasta in your lasagna and add spinach. Also, prepare healthy snacks for everyone in the family. These can include apples, oranges, nuts, berries, grapes and hard-boiled eggs.

The key is to model good behavior.

“If you want your kids to eat better, you’ve got to eat better yourself,” Colberg said.