KANSAS CITY, Mo. — Drink up, kids! That’s the message from a first national study of its kind. It finds that more than half of children and teens are not adequately hydrated.

Amie Buckner was prepared for a hot day at the park with her children.

“Wherever I go, I have a water bottle and usually they’ve lost theirs or it’s not in sight. Everyone drinks from my water bottle,” said Buckner.

It’s easier to think about hydration on steamy days. But year-round?

“We’re not sweating. We think we’re not sweating and we don’t think about drinking it as much,” said Shelly Summar, a registered dietitian at Children’s Mercy Hospital.

The new study from the Harvard School of Public Health looked at urine samples from more than 4,000 kids. More than half were not adequately hydrated, probably because they’re not getting enough water.

“Water is important for every function that the body has,” said Summar.

That includes circulation, temperature regulation and waste removal. Even mild dehydration can cause headaches, irritability, reduced physical performance and poorer school performance.

“I think it’s important when they’re really little to just give them a lot of water, and then they’re used to that, and they’re not used to having a lot of juice,” said JJ Eisfelder, a mother.

The registered dietitian says parents should set the example and drink plenty of water. She suggests keeping a big pitcher in the refrigerator.

“And I recommend adding flavor by putting in fruits and vegetables,” said Summar.

In the study, nearly one out of four school-aged kids said they didn’t drink any plain water.

So how much water should your children down? Four cups a day is adequate for toddlers. But by age 9, boys need eight cups and girls seven. Teens need even more.

Drinking water is one of the five “Fit-Tastic” habits or healthy habits that Children’s Mercy encourages, learn more at this link.