Prime Minister David Cameron left his eight-year-old daughter in the pub following a Sunday lunch, after a mix-up with his wife Samantha.
The couple's daughter Nancy wandered off to the toilets while they were arranging lifts and they only realised she was not with them when they got home, The Sun said.
Cameron rushed back to the Plough Inn in Cadsden, Bucks, where he found his daughter with staff.
A Downing Street spokesman said: "The Prime Minister and Samantha were distraught when they realised Nancy wasn't with them.
The Camerons' mistake was only discovered when the couple got home
"Thankfully when they phoned the pub she was there safe and well.
"The Prime Minister went down straight away to get her."
The Camerons were at the Plough Inn - near the Prime Minister's country retreat Chequers - with Nancy and their other children Arthur, six, and 22-month-old Florence, as well as two other families.
When Cameron left the pub he went home in one car with his bodyguards and thought Nancy was with his wife and their other children in another car.
The Plough Inn, where Nancy was left, close to the PM's country residence
Samantha had assumed her eldest daughter was with her father.
The mistake was only discovered when they got home.
Cameron drove back to the pub and found Nancy helping staff. She was away from her parents for about 15 minutes.
A Downing Street spokeswoman said the Camerons take full responsibility for looking after their children and were not blaming security officers for failing to ensure that Nancy was with the party before returning to Chequers.
The spokeswoman declined to discuss whether Mr Cameron had drunk alcohol with his meal.
"He had gone with friends at lunchtime, with a number of families with children, and they left in various different vehicles," she said.
"No-one is going to face disciplinary action. This was an error."
"They are their children and they take responsibility for them," said the spokeswoman.
Downing Street later said that it had in fact been Samantha Cameron - rather than the Prime Minister - who returned to the pub to pick up Nancy.
The Camerons and their friends were at the Plough for lunchtime drinks, rather than a meal, said a Number 10 spokeswoman.