The bodies of Neil Puttick, 34, and his wife, Kazumi, 44, from Wiltshire, were spotted at the foot of the cliffs on Sunday evening. The body of their child, Samuel, was found in a rucksack nearby.
Samuel had been discharged from hospital on Friday after it became clear he was not going to survive. He was allowed to leave so he could die peacefully at home. The boy, who neighbours said had suffered serious spinal injuries in an accident about three years ago, was confirmed dead later that evening.
A spokesman for the Bath and north-east Somerset NHS said: "Samuel Puttick had been receiving treatment for pneumococcal meningitis at the paediatric intensive children's unit at Bristol Royal hospital for children.
"When it became clear that Sam had no hope of recovery from his severe infection, he was discharged to his family home on Friday 29 May at his parents' request. He was certified dead at his home by a doctor at approximately 8pm that evening.
"We offer our sincere condolences to the relatives and friends of this family. It would be inappropriate to comment further at this stage as the matter will be the subject of an extensive investigation and coroner's inquest."
Detective Inspector Ian Williams, from Sussex police, said: "As a result of our investigation, I am satisfied that Samuel's grieving parents, Neil and Kazumi, appear to have taken their own lives.
"This is a tragic incident and we extend our sympathies to their family and to the large number of friends and carers affected."
Flowers were left at the couple's farmhouse in the village of Brokerswood, Wiltshire. One neighbour said: "They were a lovely couple and they did 150% for that boy. It is all such a shock."
Sue Capon, who runs Brokerswood country park, said everyone was still coming to terms with the tragedy. "All of them were very good friends. It's such a shame," she said. "I only saw them three days ago."
On Monday, the bodies were winched to the top of the 550ft (168 metre) cliffs, as detectives broke into a silver Volkswagen people carrier found in a nearby car park that was believed to have belonged to the group. A half-eaten banana and family-sized bag of peanuts were left on the front seat, and there was a wheelchair lift in the back. The vehicle was towed away to be examined.
An Eastbourne coastguard station officer, Stuart McNab, said coastguards on a routine clifftop patrol had seen what they believed to be two bodies about 400ft down the cliff just before 8pm on Sunday and alerted police, but it was decided it would be safer to wait and carry out the recovery the next day.
McNab, who was one of the first people to be taken to the scene by helicopter, said he had found the child's body in a rucksack along with a second rucksack filled with soft toys and a toy tractor.
Sussex police said no one else was believed to have been involved in the tragedy, which was not being treated as suspicious.
A spokesman for Dover coastguard said: "It is really horrific and incredibly sad. In my four years with the coastguard I have never known anything like this."
