A spokesman for the Metropolitan Police, which is investigating the incident, said it would not comment on whether the family had a dog.
London Mayor Boris Johnson said more must be done to tackle the growing problem of urban foxes. He said: "They may appear cuddly and romantic but foxes are also a pest and a menace, particularly in our cities.
"This must serve as a wake-up call to London's borough leaders, who are responsible for pest control. They must come together, study the data, try to understand why this is becoming such a problem and act quickly to sort it out."
Cass Barrett of London Fox Control said residents should stop putting food out for foxes or leaving rubbish around. He said he often heard of the animals coming through people's cat flats after being lured by the scent of pet food.
He said: "Foxes coming into people's houses is nothing new in my experience. Foxes are quite accomplished climbers in that a ground floor window I wouldn't imagine should cause too much of a problem for them to get in."