CAMBRIDGE — Nearly 900 children donned goggles, helmets, and sneakers to compete in the second annual New England Kids Triathlon at MIT’s Johnson Athletic Center on Sunday, demonstrating that even 5- and 6-year-olds can compete in the sport often reserved for the most extreme athletes.
“You were already on your bike when I was swimming, and then you were running,” Josephine Lee, 6, exclaimed to her sister Genevieve, 5.
It was the first triathlon for both girls.
Genevieve was race participant No. 1, the first in line to begin the race at 8 a.m. Her sister, No. 15, hopped into the pool shortly afterward.
“I was quick!” said Genevieve. Her father Jim, 36, of Brookline calls Genevieve “the competitive one.”
The Lee sisters were among the first 50 triathletes who, after a spirited morning sing-along to the “SpongeBob SquarePants” theme song, marched to Massachusetts Institute of Technology’s Zesiger Center Pool, high-fiving parents who shook cowbells and held up handmade signs bearing words of encouragement.
The swimmers, wearing blue caps and green caps, showed off computerized timing chips on their ankles and race numbers written on their tiny biceps and calves.
Close to 500 children competed in the 5- to 10-year-old category, and another 400 young people competed at the 11- to 15-year-old level.
That is double the number of last year’s participants, according to event organizer Tom Gildersleeve.
“Young kids like variety, so the swim, bike, and run combination keeps them interested,” Gildersleeve said.
He said he hopes children who go out to train will bring their parents along with them to the track and the pool.
“Your kids will get you to do some crazy things,” he said.
The youngest participants Sunday did a 100-yard swim, 3-mile bike ride, and half-mile run. The older athletes went twice those distances in each of the three segments.
Modern triathlons gained popularity in San Diego in the 1970s, Gildersleeve said, but it was after the event was introduced as an official Olympic sport in Sydney in 2000 that the competition entered the mainstream.
Professional triathlons vary in length. The Olympic race is a 1,600-yard swim, 24.9-mile bike ride, and a 6.2-mile run.
Sunday’s race was organized by nonprofit group Kids Triathlon Inc., which will organize eight races for close to 10,000 young triathletes nationwide this year. Local partners included the New England Patriots, Boston area YMCAs, and the city of Cambridge.
Fifteen-year-olds Nicole Walsh and Jennifer Ayotte, who swim for their high school team in Franklin, said their coaches recommended the triathlon as a fun way to cross-train.
“We’re most nervous about running,” Walsh said.
Ayotte added, “We’re in-the-water kind of people.”
Gavin Russell, 9, and his brother Dylan, 7, of Lincoln were among the more experienced racers.
Sunday’s race was their fourth triathlon.
“I’m a little bit tired in the legs . . . but it’s fun and it pumps you up for the next one,” Gavin said.
At last year’s event, Dylan placed first in his age group.
Minna Kim-Sams of Sudbury was watching with an experienced eye as her two daughters, Corie, 7, and Caitie, 10, competed. Kim-Sams is a member of the Boston Triathlon Team, and will be running her first IronMan — a 2.4-mile swim, 112-mile bike ride, and a 26.2-mile run — at Lake Placid in New York next week.
She began competing in triathlons in 2006.
“I had just had Corie and wanted to get in shape, and this was just one of the things on my bucket list,” Kim-Sams said. “The challenge of it,” she added, is what keeps her in the sport.
She ran a length next to Caitie toward the end of the race, snapping a photo of her daughter as the girl crossed the finish line.
“I’ve never felt so alive!” Caitie said grinning as she swung her towel over her neck and received a hug from her mother.
Racers were welcomed at the finish line by Patriots cheerleaders swishing silver pompoms, drinks, and cold towels. Many dunked water on themselves, drenching sweaty “helmet hair” that had stuck close to their heads.
Others headed straight to play on the inflatable “bouncy house” provided by the Patriots, and to coolers with free post-race ice cream.
“I was a little nervous, but they finished,” Jim Lee said as he looked proudly at his daughters, who had matching medals around their necks.
The hardest part, Josephine said, was the swimming.
“Because you stay in the water for just a second, and then you have to go up to breathe,” she said.
“The race included a lot of things kids like to do anyway,” said her mother, Nicole Prezioso, 32. “They run everywhere and play in the pool, so it wasn’t hard to put it all together.”