The night before, their home was filled with laughter as they made pancakes with their children.
As always, David and Samantha Cameron's disabled son Ivan was at the heart of the family celebration.
Yesterday the Tory leader and his wife were facing life without their six-year-old first-born child.
David and Samantha Cameron on Wednesday, just hours after the death of their eldest son, Ivan
Ivan, who had cerebral palsy and severe epilepsy, died in hospital at 6.30am after suffering seizures during the night. Doctors are understood to have tried for 45 minutes to resuscitate him.
The Camerons returned home from hospital to mourn with their two other children, Nancy, five, and Arthur, three.
Though the couple had lived every day with the knowledge that Ivan's life expectancy was low, the death of their 'beautiful boy' had been devastatingly quick. Mr Cameron told friends the only comfort he could draw was that he was with Ivan when he died.
David Cameron with son Ivan at their home in 2004
At Westminster, the knockabout of everyday party politics came to a sombre halt.
Gordon Brown led the tributes in the Commons close to tears. In the bleakest of coincidences, Ivan's death means both main party leaders now know the pain of losing a much-loved child.
The Prime Minister and his wife lost their daughter Jennifer Jane, who died in 2002 at just ten days.
Mr Brown took the extraordinary step of offering to suspend Prime Minister's Questions - the first time since the death of Labour leader John Smith in 1994 that the weekly session has been abandoned.
Instead he made a statement about Ivan, telling MPs: 'I know that in an all-too brief life, he brought joy to all those around him and I also know that for all the days of his life, he was surrounded by his family's love.
'Every child is precious and irreplaceable and the death of a child is an unbearable sorrow that no parent should ever have to endure.'
Liberal Democrat leader Nick Clegg, whose wife gave birth to their third son at the weekend, said: 'My heart goes out to David and Samantha at this incredibly difficult time for them and their family.'
Buckingham Palace said the Queen had sent a private message of sympathy. The Tory leader is expected to take at least a fortnight off work, with Shadow Foreign Secretary William Hague assuming his duties.
Mr Hague told MPs he had spoken to Mr Cameron, who wanted to pass on the family's thanks for many messages of condolence and say how 'hugely grateful' they were to the NHS staff who had helped Ivan throughout his life.
A friend of the family said: 'It all happened so suddenly.
'It had been a normal day. David had been in the office, in high spirits, and in the evening they had a family pancake day at home.
'Ivan had a bad night. He was having fits, but that is not unusual for him. But it became clear this was particularly severe and they knew they needed to get help fast.
'Then at the hospital it was obvious he wasn't going to pull through. They are shattered.'
Samantha Cameron with her son Ivan at a Yoga Centre in October 2007
The Tory leader said Ivan's smile 'could light up a room'
The Camerons' first child, Ivan was born in 2002 but by his second week, was losing weight and suffering jerky movements.
Though the couple were initially told by doctors he was suffering a kidney malfunction, Ivan was eventually diagnosed with Ohtahara syndrome - a rare neurological disorder characterised by seizures.
Doctors told the couple that some children with Ohtahara syndrome die in infancy, while others live for years but with profound disability. Mr Cameron ensured Ivan was christened at the 'earliest opportunity' because of the lack of clarity about his prospects.
Gordon Brown makes a statement in the House of Commons after Prime Minister's Questions was suspended following Ivan's death
Genetic experts told the couple there was a one in 20 chance of future children being born with the condition, though happily Nancy and Arthur are healthy.
The Camerons had to adapt their home in West London to accommodate Ivan, who needed a special lift to get him in and out of his bath.
Though his condition meant he could not move his limbs or speak, the Camerons drew strength from the fact that he appeared to respond to their love and care.
'Ivan's only self-conscious movements are to raise his eyebrows and to smile,' Mr Cameron said.
'And his smile - slightly crooked, sometimes accompanied by a little moan - can light up a room. It never fails to make me both happy and immensely proud of him.'
But asked once if he thought Ivan enjoyed his life, he replied: 'Oh, not really, I think his life's very tough.'
This Cameron family photograph was used for their Christmas card last year
The Camerons' Christmas card last year showed the Tory leader and his wife with all three of their children, Ivan cradled in his father's lap. Mr Cameron insisted that to hide his son from the public gaze would have been to deny a crucial part of what had shaped him as a man and as a potential Prime Minister.
Relying completely on the NHS for his son's medical care, colleagues say, focused his mind on the importance of the state-funded service. 'When your family relies on the NHS all the time - day after day, night after night - you know how precious it is,' he said.
Mr Cameron also voted in favour of controversial embryo experiments in the hope that they might lead to treatments for his son and others like him.
Tory schools spokesman Michael Gove, a close family friend, said: The interaction between David, Samantha, Ivan and the other children was something that anyone who came into contact with them found uplifting.'
David and Samantha with daughter Nancy (on shoulders) and sons Ivan (left) and Arthur shopping in Portobello Market in London
Mr Gove said coping with Ivan's disability had been a 'huge and wrenching change' for the Camerons.
But he added: 'David and Samantha coped amazingly. I saw them at difficult times maintain the strength of their relationship.
'David and Samantha often had to take Ivan to hospital for treatment. It was often the case that they would have to spend the night or long days with Ivan in hospital while he was getting a very, very high quality of treatment.
'They would spend nights sleeping on the floor alongside him.'
The Camerons asked that, rather than sending flowers, wellwishers should send donations to Mencap, the Friends of St Mary's Hospital or one of three other charities - Friends of Jack Tizard School; Helen & Douglas House, Twickenham; or Shooting Stars House, Hampton, Middlesex.