Three-year-old Sam Tuckett from Sheffield was enjoying a family day out in the Peak District in March - walking a few steps ahead of his parents with his older brother - when he suddenly disappeared.
Sam had fallen through a 40cm-wide opening in the ground, which is the same size as an A3 piece of paper.
He fell six metres, hitting his head and body on the rocks as he fell.
Mum Louise, 36, recalled the horrific moment.
She said: “My husband and I just looked at each other in complete panic.
“My husband Mark clambered down to get him, which made our one-year-old daughter scream as she didn’t know what was going on.
"Our eldest just asked if Sam had died- he doesn’t really know what that means yet, he just knows that it’s the worst thing that can happen.
"I told him everything was going to be okay, but I honestly didn’t know if it would be.
“I called 999 and they asked me lots of questions- was he conscious, could he move, was he breathing?
"I couldn’t see Sam, so I couldn’t answer any of them.
"I was frantically flagging down any passers-by in the hope that one of them would be a doctor or nurse and be able to help, but none of them were.”
When his dad finally managed to bring him up to the surface, Sam was bleeding heavily and crying.
He carried him to the nearest road while the family waited anxiously for an ambulance.
It arrived 15 minutes later, and Sam was taken to the Emergency Department at Sheffield Children’s Hospital.
Louise added: “It sounds strange, but I felt better when we were on our way, because I knew they were the only place that could really help him."
Sam was rushed into the Emergency Department on a trolley and taken through to the resuscitation area, where more than ten members of staff surrounded Sam, each checking on one aspect of his health.
“It was very crowded, and we had to be careful, making sure to keep out of the way and not trip over wires going in every direction. Everything goes through your mind- I was planning for the worst possible outcomes.”
For the first few hours, Sam was unable to speak.
He underwent a CT scan to determine the extent of the damage to his brain.
Shortly after, Sam told his Mum he wanted to go home.
Louise added: “The feeling of relief was immeasurable- he was talking and thinking like the boy we know.
"For the first time, I had a genuine glimmer of hope that he would be okay. Sam could hear us talking and telling him we were with him.
“Both my husband and I held onto the though that he’d have heard us saying we loved him, and we were staying with him while the nurses and doctors saved his life.”
Eight hours would pass before Sam was stable enough to be moved onto a ward at Sheffield Children’s Hospital and five days later, he was discharged.
Proud mum Louise said: “Sam is a bundle of energy who believes he can do anything. He has no memory of the accident, but it was a day that the rest of us will never forget. We owe everything to every member of staff who helped our family in those days.”
Sam’s family are now backing The Children’s Hospital Charity’s £4.5m appeal to transform the Emergency Department at Sheffield Children’s Hospital.
The department was built to see 32,000 children every year but now sees more than 60,000 every 12 months; from across South Yorkshire, Derbyshire and Lincolnshire.
Louise said: “We experienced first-hand that the Emergency Department needs to be developed. The care was fantastic, but we never realised how well the staff manage with the limited space. We want to help them build a place which has all the facilities they could possibly need, because our story could happen to anyone."
To find out how you can support the appeal for a new Emergency Department at Sheffield Children’s Hospital, visit www.tchc.org.uk/donate