Well, that is if you believe this in the Daily Mail :
"Both David and Samantha Cameron were left red-faced when they accidentally left their eight-year-old daughter Nancy in the pub.
the Prime Minister's wife has revealed it was in fact her who was
responsible for the mistake after failing to check the female toilets.
couple drove off from The Plough Inn in Cadsden, Buckinghamshire, in
separate cars - both believing Nancy was with with the other."
"The Prime Minister was driven back to
Chequers, which is two miles from the pub, with protection officers in
one car, while Mrs Cameron drove their other children in another.
Cameron presumed that Nancy was in the car with his wife, while she
thought that their daughter had jumped in with the Prime Minister."