At 6, he completed his first triathlon, but that was just one of his pursuits. He loved baseball. He was in the Cub Scouts. He looked forward to the kids' workshop at the local Home Depot.
"We are thankful to the Lord for giving us seven years with our beautiful loving son. It is with heavy hearts that we return him," the family said in an obituary.
Jesse Lewis, 6
Jesse loved math, riding horses and playing at his mom's farm, his father told the New York Post.
"He was just a happy boy," Neil Heslin said. "Everybody knew Jesse."
He told the newspaper that his son was to make gingerbread houses at school Friday. Heslin was planning to help.
Instead, the last time he saw his son was when he dropped him off at school at 9 a.m.
"He was going to go places in life," Heslin told the Post.
Ana Marquez-Greene, 6
"One, two, three, ready and go," Ana counts down in a homemade video provided to CNN affiliate WTIC.
The girl in pigtails stands in front of a piano as her brother plays. Her voice is clear, bigger than her size. Ana smiles and waves.
Her father, Jimmy Greene, is a jazz musician. His representative released a statement on Ana's death, describing the little girl as "beautiful and vibrant."
"The family has requested privacy at this time of heartbreaking loss," it read. They "have asked us to relay their sincere gratitude for the outpouring of support and sympathy locally, nationally and internationally."
James Mattioli, 6
As he was quick to remind everyone, James was 6 and ¾.
"He loved to wear shorts and T-shirts in any weather and grab the gel to spike his hair," his family said in a loving obituary. "He would often sing at the top of his lungs, and once asked, 'How old do I have to be to sing on a stage?' "
Indoors, he spent his time playing games on the iPad -- especially the lawn mowing one. Outdoors, he loved to dive off the diving board, "swim like a fish" in his grandfather's pool and ride his bike -- without training wheels, mind you.
"I need to go outside, Mom. I need fresh air," he would often say.
He was born four weeks early -- because he was hungry, his family joked.
James had a voracious appetite. His favorites? His dad's egg omelets with bacon, and his mom's French toast.