The PM warned journalists visiting Downing Street that if their scalps started itching it was down to his daughter Nancy, seven, and son Arthur, four.
The youngsters have been treated with medication and are using an extra fine comb to get rid of the blood-sucking lice.
Asked about the nits, Mr Cameron told the reporters: "If you find them when you get home I apologise. Let me know and I'll send you a comb and some ointment."
The news comes a week after pest control experts were called to Downing Street to get rid of rats. A rodent had been spotted outside No 10 on TV news.
But nits are not associated with dirty heads - they live in any hair where they can feed on the scalp. They are normally caught by children when they attend primary school.
The PM's spokesman was asked if the Cameron children's head lice problem had spread to other members of the family - David, wife Samantha or baby Florence, six months.
He said: "It's contained at the present time."