A nurse caring for sick children at Great Ormond Street Hospital (Gosh) described the moment they wake up to presents on Christmas Day as "the best feeling in the world".
Hannah Sharman, a senior staff nurse caring for children with heart conditions on 24-bed Bear ward, described how she and her colleagues lay out gifts for the children overnight ready to be unwrapped in the morning.
Ms Sharman, who has worked four overnight shifts ending on the morning of the 25th, said it was a really difficult time for youngsters to be in hospital but that her team did all they could to make it as Christmassy as possible.
This year, up to 250 children are expected to wake up on Christmas morning at Gosh, the hospital said.
The 28-year-old, from east London, said: "I will always give up any of my time to be with the children who are unfortunate enough to go home and spend Christmas with their families.
"Just being able to put out the presents for them and watch them wake up in the morning with a smile on their face, it's the best feeling in the world."
"It's always a pleasure to be part of their special day," she added.
To mark the day, staff don silly hats and reindeer antlers and play games with the children, who received a very special visit from Santa in the days leading up to Christmas.
Children that are well enough can have Christmas dinner in the Lagoon canteen, while those who are most sick will have a tray brought to their beds.
Families, patients and staff are also invited to attend a Christmas Eve carol concert and midnight mass in the hospital chapel.
Three-year-old Esme has aortic stenosis, a narrowing of the aorta, and is in Gosh waiting for a transplant.
Her mother, Linda, from Reading, said: "At Christmas we want everyone to be happy, as healthy as they can be and be together.
"In the new year we hope Esme will get her new heart and continues to become better, is thriving, and ultimately we would like her to get home."
"We couldn't express our gratitude to the nurses and staff at Gosh enough for the care they have given Esme, and continue to give to her and our family.
"There is no way we could thank them enough."
James Linthicum, senior chaplain at Gosh, said the hospital does "everything humanly possible, short of having a baby in the manger" to ensure children of all faiths and backgrounds can enjoy the magic of Christmas.
Mr Linthicum will be doing his 11th Christmas Day ward round this year, accompanied by a Muslim chaplain and, for the first time, a rabbi.
He said: "A director of nursing who's no longer with us used to say 'Once you establish the fact that nobody wants to be here, then it's the greatest place in the world to be'.
"So if you start from that point, it is an amazing place. Everybody makes an effort. The nurses make an effort, the doctors, the families.
"We have siblings come in, Father Christmas visits normally ... I can tell you where the chimney is, it's in the old building, that's the one he comes down. And it's just an amazing sense of being in it together.
"There's a sense of hopefulness, and really for me, I use a phrase from O Little Town of Bethlehem, this is a place where the hopes and fears of all the years meet.
"Parents are hopeful because this is one of the most amazing hospitals in the world, but it's also fearful because your child has to be in one of the most amazing hospitals in the world."
Addressing patients and former patients he said: "You're amazing. Christmas would not be Christmas for me, much as I'd like for you all not to be here, the fact that you have been and are, you make it probably the most meaningful day of the year, by your willingness to either muddle through or rejoice in it or even share difficulties.
"But the fact that you're here and that we all share a hope of some kind is a true blessing, it's my Christmas gift."
He said he hoped everyone could draw from Christmas the message of hope, adding: "I hope the children realise what gifts and blessings they are to us."