He described it as the "worst job" he's done in his 22-year paramedic career.
"The worst thing any emergency service person could go to is your own family and not even know it."
Benjamin's head bounced off the road, ripping off his helmet, and a second impact meant his bare head hit the road.
Even more concerning as they approached the site, was knowing there had been a fatal crash near the scene in May 2015.
Allen's actions of flicking his bike around to throw Benjamin clear, probably saved their son's life, his mother Robyn Butler, a nurse at Starship Hospital, told Fairfax.
Meanwhile, at the scene, as Marlow knew it would be tough treating his son, he offered to assess him while Butler tended to his brother-in-law.
"I could hear Benjamin screaming, so I knew he was with it," Butler said.
Benjamin suffered a serious concussion and broken collar bone, while Allen suffered 14 breaks in seven ribs, a punctured lung, fractured collar bone, scapula and shoulder blade, and a concussion.
As Benjamin was going to be okay, Butler took over treating his son as they headed off to the hospital.
Benjamin was off school for two months and monitored by Auckland Brain Injury Rehabilitation and then went for a follow-up with a child psychiatrist.
Three months later he was given the all clear, but still suffers the effects.
Benjamin's uncle spent 10 days in hospital, was off work for three months and is still recovering from his injuries.
"But they are both still alive. People have died from less," Phil Butler says.
He says the rescue helicopter was a godsend and helped save people's lives everyday.