Sorry but they drive me mad. I drive carefully all the time so I'm not going to take special care if there is a baby in the car in front of me. Or are they alerting me to the fact that the person in front of me is likely to drive erractically as they are a parent and therefore have much more important things on their mind than driving safely? Or are they, as I suspect, just a way of saying 'Hey look what I made...'? And don't get me started on the ones that say 'Princess on Board'. They don't even make me laugh.
Anyone else want to put them in Room 101?