Extreme heat poses health risks to everyone — and it's a unique challenge for kids who love to be outdoors in summertime. Small children can be especially at risk in the heat, but experts say they can still play safely — if grownups follow a few guidelines.

Extreme temperatures can cause dangerous stress to the heart, kidneys and other organs, and humidity and dehydration can compound the risks. People can also sustain burns from pavement and other surfaces — including playground equipment.

Several factors put children at risk from heat, from physical characteristics to the likelihood that they're not attuned to notice signs of their own heat exhaustion. One basic rule to keep in mind is that the younger they are, the more carefully they should be monitored.

Here are some tips from experts, for people looking after small children and big kids:

Think of small kids as potatoes

Children under 9 can be at a particular risk for heat stress. Part of the reason is behavioral — many kids can get so distracted that they might not notice the effects of high temperatures — but other factors are physical.

"Imagine that you had a potato and you want to cook that potato," climate scientist Camilo Mora, a professor at University of Hawaii at Manoa, told NPR.

If it's a big potato, heat will have a hard time getting to its core. But smaller potatoes cook much faster, as heat can quickly reach their center.

"That's exactly what happens with the kids," Mora said. "The kids are like the small potato in which the heat can get faster to the core. While in an adult, that heat had a harder time getting to the middle and cooking us."

That makes kids more vulnerable to high temperatures. Another mechanism is the way they handle water.

"Children's bodies take longer to increase sweat production and otherwise acclimatize in a warm environment than adults' do, research shows," according to KFF Health News. "Young kids are also more susceptible to dehydration because a larger percentage of their body weight is water."

Look for changes in kids' behavior

It could signal that the child is in distress from too much heat.

"One of our biggest signs is kids who are normally upbeat and having a great time and are really in it are not [doing that]," nurse Camille Hatcher of the Lake Nixon Summer Day camp in Little Rock, Ark., recently told NPR.

Hatcher says her camp "is 100% outdoors," but it has added a cooling spot where kids can play cards. Staff also direct campers toward shade and swimming — and they look for kids who seem out of sorts, and even irritable.

"These are all signs of a kid who is not feeling well but is not able to communicate it," Hatcher said. "They can also complain of, like, 'Oh, my tummy hurts. I don't feel good. I want to go home.' "

When staff notice those signs, Hatcher said, they get the kids away from the sun and heat.

A bit of water can help cool a child in a stroller

Infants can struggle to regulate their body temperature. And while many parents drape a thin muslin cloth over strollers to give shade to babies, research suggests that can actually make the temperature inside the stroller hotter — by as much as 7 to 9 degrees Fahrenheit.

Instead, parents should try wetting the cloth, according to Ollie Jay, a professor of heat and health at the University of Sydney.

"What we found is that if you then wet that cloth, it cools the temperature inside of the stroller to approximately 4 degrees Celsius below what it is in the shade outside," Jay said.

In Fahrenheit, that's about 7 degrees cooler. So while it's best to keep babies in a cool room indoors when temperatures reach high extremes, if they're outdoors in a stroller, a wet thin cloth on top of their stroller can act as a sort of makeshift AC unit.

A few steps can help kids (and adults) cool down

Finding shade and, ideally, an air conditioned space are best. But kids who develop a headache, dizziness or lethargy from the heat need to cool down — fast — and drink water.

"A 10-minute cool shower can effectively lower your internal body temperature. If you are in a situation where you lose power and don't have air conditioning, that's one way to do it," says Ashley Ward, director of the Heat Policy Innovation Hub at Duke University, on a call with journalists about the heat.

Ward and other experts say immersing feet in cold water is another quick way to lower core body temperature. She also notes that even plunging your arms into water past the elbows has been shown to help.

When our bodies reach a core temperature of about 104 degrees Fahrenheit, that's a sign of heatstroke.

Make sure children stay hydrated

Kids should have water before they head out. In general, when tweens are active outside, they should drink water frequently — 3 to 8 ounces every 20 minutes — and older kids should have up to a liter or more (approximately 34 to 50 ounces) each hour, according to a guideline from the American Academy of Pediatrics.

Here are a few more tips:

• Avoid sugary and caffeinated drinks in extreme heat — they can cause dehydration.
• Our bodies' hydration level is reflected in our urine. A light yellow color is fine; dark yellow or orange suggests the body needs more water.
• "If you are sweating a lot, combine water with snacks or a sports drink to replace the salt and minerals you lose in sweat," the Red Cross says.

If kids in your care are tired of water, milk can also be a good choice, especially for young athletes, as it contains protein, vitamin D and calcium.

"After a hot practice, drink enough water to be able to urinate. Then drink 8 ounces of milk after some cooling off time inside," the University of Kansas Health System recommends.

Speaking to the kid in all of us, it adds, "Chocolate milk with a minimal amount of sugar offers some carbohydrates as well and may be more desirable than plain milk."