It was barely sunrise and Michael DeMasi jnr was romping through the corridors at a children's hospital in Philadelphia, balancing on a red line that was etched into the floor design and telling his mother to tie a balloon to him so he could "fly."
The 4-year-old boy fancied himself a real-life superhero, wearing a blue T-shirt with photographs of his 4-month-old twin brothers, who were born with a rare immunodeficiency disease.
Michael's little brothers - Santino, "Sonny," and Giovanni, "Gio" - needed a bone-marrow transplant, and when his parents told him that he was a donor match, Michael told them that he wanted to save his brothers and would give them some of his.
"Hey, Michael," his mother, Robin Pownall, called out as she filmed her young son early one Thursday morning in March, running ahead of her through Children's Hospital of Philadelphia (CHOP).
"Yeaaaah?" he responded, hanging back to let her catch up.
"You ready to go?" his mother asked.
"Yay!" he said, pumping his fists and jumping up and down.
"Where you going?" she asked him.
"To save my baby brothers," he said.
"To save your baby brothers?" she repeated. "You're the best."
The preschooler knew what was about to happen, his mother said - a long needle would be pushed into the bone near his hip to extract the marrow, then the cells would be transplanted into his brothers.
He did it anyway.
And later in the day, when his brothers received the stem-cell infusion, Michael was there to watch, jumping and shouting, "That's my bone marrow! That's my bone marrow!" his mother said.
Nearly two months after the procedure, the twins were discharged last week from the hospital. Their mother posted a video on Facebook, showing Michael wearing a superhero T-shirt, smiling and standing between his little brothers.
"I saved you guys," the preschooler said. "It's time to go home."
Santino and Giovanni were born in October with Chronic Granulomatous Disease (CGD), an immune disease in which the immune system does not work properly, meaning even a common cold could become life-threatening, their mother told the Washington Post. She and her fiance, Michael DeMasi, were already familiar with the condition. Their oldest son, Dominick, 9, was also born with GCD and they knew it was a possibility that their other children would be born with the disease.
Following his diagnosis only weeks after his birth, Dominick was put on a transplant list and received stem cells from the umbilical cord of a donor. He is now considered cured, his mother said.
When the twins turned out to have CGD, Michael, who was not born with the condition, was tested and found to be a match. His parents talked to their doctors about the risks, such as pain and soreness and complications from anesthesia, then they sat down with Michael and tried to explain.
Michael knew that his little brothers were sick and he knew that they needed bone marrow. He also knew that he had been tested to determine whether he was a match, his mother said.
When his parents told him he was, he exclaimed, "I'm the match? I'm the match?" Pownall recalled.
His parents asked him whether he wanted to go through with the donation.
"We were straight up - 'It's going to be a big needle going into your back, bud,'" Pownall said she told him. "We asked him, 'Do you want to do this? If you're scared, you don't have to.' "
Pownall said her son asked whether his bone marrow would allow his little brothers to come home.
She said yes.
He said okay.
Pownall said her son told her he wanted to "help save my baby brothers."
But Pownall said the decision was not simple - she and her fiance grappled with the option, wondering whether Michael understood what was being asked of him and whether it was right to ask him at all.
"Part of me was like, 'Well, he's 4. Maybe he doesn't know what's going on.' But he did, and he was all for it," she said.
Doctors told them that bone marrow from a matching family member was the best choice.
Art Caplan, a professor of bioethics and head of the division of medical ethics at the New York University School of Medicine, said situations in which children are the donors do present ethical questions, namely whether a child can truly understand the risks and grant their permission - a principle known as informed consent.
On March 8, Michael marched down to the hospital's patient check-in area.
His mother had told him that he was going to be "a real-life superhero," and the small boy who loves Captain America as well as Spider-Man, Batman and Superman seemed excited to join their ranks.
The children's aunt wrote on a GoFundMe page that Michael and his brothers were doing well.
"Michael did his procedure this morning for them to take the bone marrow cells," the post read. "He is perfectly well, playing and all like nothing happened. Giovanni received the bone marrow cells around 2:30 pm & then Sonny received the bone marrow cells around 5:30 pm. Both babies are doing well and sleeping. Now is time for their bodies to heal, with the new bone marrow cells to build up a healthy immune system."
She posted an update last week, saying the transplants were successful and the twins were home.
Pownall said that now the twins, who are nearly 7 months old, show no signs of Chronic Granulomatous Disease, though their doctors are monitoring them closely.
Michael told the Post: "I saved them because I'm a superhero!"