Usually, at the end of a week at YMCA Camp Kern in Ohio, kids gather around a bonfire. But this summer, it’s way too hot.

One humid day, temperatures hit 92 degrees. Kids wiped sweat from their foreheads even as the Sun began to set. Campers crowded around water coolers to refill bottles. They fanned themselves, trying to get a breeze going.

There are over 20,000 summer camps in the United States. About 26 million campers show up each year. Many camps have had to adapt to extreme heat this summer. The heat isn’t just uncomfortable. It can also be dangerous.

Heat affects children differently than adults. Children’s bodies can warm faster than adult bodies do. And it can be tough to remember to drink enough water while doing fun activities like rock climbing and obstacle courses.

Still, grownups also have to watch for signs of heat-related sickness like heatstroke. Lizzy Johnson went to Camp Kern several times while growing up. She’s back now as a counselor.

Ms. Johnson remembers the fun she had as a child—but not the heat. “I never remember being this uncomfortable,” she says.

Camps find ways to make sure campers stay safe and enjoy the summer. Camp Kern switched up its usual schedule. Leaders added more breaks and indoor sessions. Water-based activities like swimming help keep campers cool. The pool is open all day.

Meanwhile, many kids crank up the air conditioning inside cabins. Some carry paper or small electric fans. Others pour water on their heads throughout the day. They rush forward when camp workers hand out refreshing, ice-cold popsicles.

As a deer pants for flowing streams, so pants my soul for you, O God. — Psalm 42:1