Supermarket + children = headache

I've had a lovely relaxing weekend. Three days off work and the last two spent in the excellent company of Voley (and I even managed to pull back a scrabble win). However, five minutes in the supermarket and I felt like screaming. Why do parents allow their children to run around the aisles like they are in a playground and to dictate to them what goes in the shopping basket..."I want these cakes, they have more sugar in them"- no, you clearly don't need any more sugar. My head was throbbing by the time I had finished. I was rather amused though by the child who wanted to know how wood is made- her mother's answer was that it comes from trees but this quite obviously didn't satisfy the child who continued to ask "but how is it made?".