Tony Blair and his colleagues call 10 Downing Street "The Tardis" owing to its deceptively spacious interior, the prime minister told TV show Blue Peter.
Mr Blair was answering questions from the viewers when he explained the house is bigger on the inside than it seems.
He also revealed his favourite meal to cook was spaghetti bolognese.
The interview was recorded in July, weeks before a leaked memo revealed his appearance on the show was part of the strategy for his last year in office.
The memo, apparently from some of Mr Blair's advisers, also revealed plans for the prime minister to appear on Songs of Praise and Chris Evans's radio show.
An 11-year-old Blue Peter viewer called Christopher wanted to know if the inside of No 10 was bigger than it looked from the outside.
Mr Blair responded: "Yes, I mean a lot bigger, we call it like the Tardis.
"What happens is you come in and you think you're just coming into a house ... then there are several flats and there's about 250 or 300 people that work here."
And he confirmed to presenter Konnie Huq that he and his family actually live above Number 11 Downing Street.
And when asked by a 12-year-old called Amy to recall his best and worst experience in office, he said the most "extraordinary" time of his Downing Street tenure was in July 2005 with London winning the Olympics followed by the suicide bomb attacks on the capital's transport network.
Blue Peter will be broadcast on BBC One at 1700 BST.