A group of Beaver and Cub Scouts will qualify for a unique badge - by camping out in the garden of 10 Downing Street.
The youngsters have pitched their tents on the Prime Minister's lawn to help raise cash for children's health charity Sparks.
Games have been organised and meals will be prepared in the grounds, where US President Barack Obama manned a barbecue earlier this year.
Aged between six and eight, the 15 boys and girls are members of the Broomwood Beaver Colony of the 12th/14th Battersea Westside Scout Group, from south London.
Assistant leader Fiona Williams said: "This is the first time I have been on a sleepover as a leader with the colony and I am very excited to begin the experience by camping in the garden of No 10 Downing Street."
For many of the children, the "sleepover" will be their first night away from home.
As well as being given a tour of the inside of the residence, they will get a badge featuring Number 10's famous front door to display on their uniforms. It was designed by the group's leader Harvey Ward, who will be supervising their stay along with three older cub scouts.
Mr Ward said: "The Scout Family is an amazing organisation. It helps equip young people with great skills and teaches them new things. In fact, when they learnt how Sparks helps newborn babies, the group decided to raise money for the cause.
"Scouting relies on volunteers, and while we have a huge waiting list of children, it would be fantastic if more Leaders could join in the fun too.
"I am sure the Beaver sleepover is going to be an amazing experience for all involved, and something the children will remember for the rest of their lives. How many people can say they have slept in the back garden of Downing Street?"