Five years after a bone-marrow transplant saved little Carter Nicolai’s life, the third-grader ventured out alone on a kid’s-sized ATV to an open swath of land in view of his family’s Dakota County home, rolled the vehicle and died.

The crash that took the life of 9-year-old Carter occurred Tuesday behind the 29100 block of Curtis Lane on land where homes are being built for later sale as part of student instruction by the Randolph School District, according to the Sheriff’s Office.

Carter overcame a serious autoimmune disease, aplastic anemia, which required a bone-marrow transplant, said his aunt, Caryn Riley.

“It’s hard to explain, not fair,” Riley said less than 24 hours after losing her nephew, who yearned to follow in his father’s footsteps into farming and enjoyed anything to do with singing, dancing or tractors.

“He lived life to the fullest and was able to live carefree” thanks to the transplant, she said. “We got five more years. It wasn’t enough.”

Carter was born on the Fourth of July, 2010, and his disease was diagnosed in September 2014, two months after his fourth birthday, Riley said. The fortunate find of a bone marrow match led to the successful transplant in February 2015.

Carter, who was wearing a helmet, was riding the vehicle over dirt piles and unaccompanied across the street from his home, where he became pinned under the ATV in the open area, said Chief Sheriff’s Deputy Joe Leko.

Other youngsters came upon the scene and called authorities about 6:30 p.m., Leko said.

Deputies arrived in less than 5 minutes and were joined by an off-duty nurse and a firefighter in providing lifesaving efforts to the boy, who was declared dead at the scene, Leko said.

District Superintendent Michael Kelley said there are no postings limiting access nor any barriers to prevent anyone from going on the property, where the second of eight homes is under construction.

While the work continues, students have been kept off the site amid state-imposed limits on face-to-face education in the wake of the coronavirus outbreak.

“You always think back and look” at what could have been done to prevent such an incident, Kelley said, who added that the boy attended third grade in his district. “We’ll obviously, look at a lot of things. We’re just taking it a step at a time.”

Chief Deputy Leko said Carter’s mother was running an errand and his father was at work when Carter rode to the lot outside his front door.

“He had to cross a road and another private property to get there,” Leko said. That said, he noted that “it’s a rural part of the county. It’s what kids do. ... Just tragic.”

An online fundraising effort on behalf of parents Sandy and Brian Nicolai and three siblings has been started and is sure to surpass the initial goal of $15,000.

“He was amazing,” Riley said. “He was a Fourth of July baby, and to explain him as a firecracker is spot on.”