It's reassuring to know that other parents have found their cars turning into discomfort zones of philosophical discussion. Last week, I criticised the Barnardos billboard campaign, which aims to raise parenting issues, but also challenges children to think about distressing experiences - such as parents fighting or falling sick.

Barnardos told me that I was the first parent to complain. Readers have responded and one parent writes: "I agree with you totally. Many mornings I spend in the car, discussing serious and complex issues with my 10-year-old daughter. And that is at 7.30 in the morning with two smaller children in the back of the car, listening. Those discussions often are triggered by posters on the roadside (we have covered Sellafield and atom bombs, abortion, child abuse...).

"While I think it is right to answer your children's questions and be open with them, I have often struggled to explain things which a 10-year-old perhaps should not be burdened with. Add to that topics that are brought home from school and you find yourself deep into ethics and philosophy. The Barnardos campaign raises more issues. Do we really need all this?"

Much advertising doesn't take children's needs into account. Another example: billboards near schools telling us how great alcohol is. In the absence of a child-friendly ethos in advertising, the only solution would seem to be never to step out the door and turn off the TV.