More than £150,000 has already been raised to create a purpose-built centre for children with complex disabilities or life-limiting conditions.
Charlie House announced its Big Build Appeal last week, which hopes to raise £8 million to get the centre up and running.
At the beginning of the campaign, it was announced that £1m had already been earmarked for the centre.
At a private dinner, an anonymous donor pledged £150,000 which covers the costs to build one of the children’s bedrooms.
Charlie House launched plans to build the centre, which will be the first of its kind in the north-east, earlier this month.
It will comprise of eight specialist bedrooms for children, as well as a number of different facilities, such as a sensory room, library, spa pool, craft room, teen den, soft play area, therapy room, star room for end-of-life care and bereavement, outdoor play area and sensory gardens.
There will also be room for families, and it will provide much-needed respite care, for those who currently have to travel more than 100 miles to Kinross to access suitable care.
Susan Crighton, director of fundraising at Charlie House, said: “Following our drop-in launch event for the Big Build appeal on Wednesday, we held a dinner to celebrate the campaign.
“At the end of the evening we received a wonderful surprise in the form of an anonymous donation of £150,000 to cover the cost of one of the children’s bedrooms in the new specialist centre.
“This really was the icing on the cake to our launch day and we are extremely grateful to our donor for this life-changing gift.
“The days which have followed our launch have been so humbling with many people getting in touch to donate towards our campaign.
“From an elderly gentleman who popped into the office with a donation, to people who have been donating via our website and people pledging future support, it has truly shown that the north-east gets behind initiatives which will support the north-east.
“We couldn’t have asked for a better response to the Big Build Appeal and we are excited to see how it progresses.”
Charlie House is also encouraging people to sign up for the charity’s Santa Fun Run as part of the city’s Christmas Lights switch-on this Sunday.
Families will be running or walking the length of Union Street in less than 30 minutes dressed in Santa outfits, and the event is accessible to wheelchair users and their parents or carers.
All proceeds will go towards the Big Build Appeal.
Costs to enter is £10 per adult, £10 per child, £35 for a family of two adults and up to three children, and £10 for wheelchair users and their parents or carers.
Included in the costs of signing up is a bib number, Santa suit and medal.
You must be 16 or over to register yourself, those under 16 must be entered by a parent or guardian.