Then she moved to senior school and a wirier, more troubled-looking policeman appeared. "No doubt about it," he told the girls, "you are going to get mugged and you might get assaulted." He taught them how to hand over a mobile phone without provocation. He advised them to carry money to give away because, occasionally, frustrated mugger equals murderer. The lesson was to stay alert, avoid conspicuous gaiety and never catch a stranger's eye.
A few weeks ago, she was visited again, this time by self-defence instructors. When asked about the legal limits to fighting back, they said:
"Better be tried by 12 than carried by six." They also said: "Let him have your property. Don't let him have you." Should my daughter be groped on the underground, she now knows to lift the man's arm in the air and say: "Look at this dirty old man." If she is sexually assaulted in the street, she has nifty karate moves. There is no training against guns and knives.
Still, she comes home confident after self-defence lessons. Her older brother looks at her with admiration and unease. He has been mugged with dreary regularity. Recently, he saw two older boys on bikes watching him from the corner of the road. Experience taught him to run. The boys'
experience taught them that liberal, middle-class boys are cannon fodder.
One shouted: "Why are you running away? Are you being racist?" My son returned, mortified. As he was assuring the boys that he abhorred racism, one of them hit him to the ground and demanded coins and phone.
So how should schools portray the world to their pupils? The educational ethos tends to be optimistic about human nature. It is positive about teams, communities and citizenship. I prefer this to "fear your neighbour".
Schools represent sanctuary, but they should not be a parallel universe.
Whether it is local crime or global terrorism, the threat must not be dismissed or exaggerated. Politicians have a duty to children not to distort crime statistics or terrorist threats.
What do politicians - and teachers - want children to think the world is like? The picture they already have is pretty confused.
Sarah Sands is a journalist and writer