UPDATED 01/30/12 6:30 a.m.

CHICAGO (CBS) — Children’s Memorial says it broke a record for fundraising Sunday, as 3,000 people climbed to the top floor of the Aon Center to raise money for charity.

They walked up the stairs, all 80 flights, to raise money for Children’s Memorial Hospital. It’s the 15th annual “Aon Step Up for Kids.”

LISTEN: WBBM Newsradio’s Steve Miller reports

Two of the climbers – Jon Mooney and Steve Greenberg – stood at the stairway door at the top after they finished – and watched others as they emerged on the 80th floor.

They said the key is for climbers to pace themselves so that they can finish without stopping.

Lisa Watters was the leader of the group called “Benny’s World.”

“Benny was my son. He was treated at Children’s Memorial for a brain tumor, and he passed away a year and a half ago,” she said. “So we raise money to try to find a cure for pediatric brain tumors.”

Benny’s World hoped to raise $1,500.

Meanwhile, firefighter Mike Hiemer and some of his buddies at the Bedford Park Fire Department made the climb in full gear.

“I had an air pack, which is roughly about 25 pounds; full turn-out gear, which is maybe 10-15 (pounds) with the helmet. So you’re looking at about 30-40 extra pounds,” Hiemer said, “and I already weigh like 260, so it’s a lot of weight going up.”

Hiemer says it was not an easy trip up, especially around floor 50.

“We had contemplated wearing gym shoes; decided to wear bunker shoes,” he said. “One of the driving things – because it was for the kids — as dumb as it may sound — we said that on 9-11, those guys didn’t have a chance to take off things, so why should we.”

Organizers said this year’s Aon Step Up for Kids was their biggest ever, raising $575,000.