AUBURN — It’s a crazy world and things seem to change by the minute, but there’s one thing you can always count on: children and bikes.

They were a big part of the Dempsey Challenge warm-up Thursday when 40 kids got together at the Auburn-Lewiston YMCA with a legend in the world of bicycles.

Fast Freddy Rodriguez was on hand to teach the kids biking safety and to stress the joy of riding.

“Cycling,” said Rodriguez, who came from Berkeley, Calif., for this weekend’s Dempsey Challenge, “is something you can do all of your life.”

Like he had to tell the kids.

Wearing helmets that they got to take home, the third- through sixth-graders looked right at home on borrowed bikes in the YMCA gymnasium. They rode obstacle courses and participated in races during which the slowest rider was declared the winner.

“I’ve been riding bikes my whole life,” said one fourth-grader as he wheeled across the gym.

Rodriguez has participated seven times in the Tour de France. He competes in races all over the U.S. and Europe. To anyone in the world of cycling, he’s a star.

“This guy’s job is to ride a bike every day,” said Jim Tasse, education director for the Bicycle Coalition of Maine. “How cool is that?”

Mia Arvelo, a 5-year-old on a pink bike, almost ran into trouble a few times as she mugged for the cameras while breezing across the gym. She stayed upright, though, because she’s a kid and kids just know how to ride.

The bicycles, 25 of them, will be given to local groups and donated to needy children.

Tess Caldwell, fundraising coordinator for the three-day Dempsey Challenge — a fundraiser for the Patrick Dempsey Center for Cancer Hope and Healing that begins Friday — took to high ground on a row of bleachers and watched the children ride. These children, she mused, might grow up to be active participants in the annual challenge, which this year so far has drawn more than 4,000 registered participants.

Of course, it never hurts to have stars like Patrick Dempsey and Fast Freddy chipping in.

“They both have such passion for this,” Caldwell said.

She said a few more things about the event, but like most others, after a while she became mesmerized by all those kids whizzing by on all those bikes.

“This,” she said, “is just really cool.”

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