I haven't shopped regularly in a supermarket for seven years. My moment of truth came on a commercial farm in East Africa where I saw green beans and other vegetables being harvested for a well-known supermarket supplier.
The crops were sprayed and irrigated, but behind the scenes, at the back of the farm where the farm workers lived, there was one water tap for more than 100 people, and no toilet facilities. Nor could their children go to school; the farm was too isolated.
Food production in many places is like this - the crops better cared for than the people who harvest them. And then the produce is encased in plastic, flown to the UK, and carted across the country in giant lorries - global warming gone mad.
How do I manage without a weekly shopping trip? Well, I use local shops and the farmer's market, where I buy mainly seasonal produce. I also buy Fair Trade products. We have an allotment and grow fruit and vegetables.
Like many women, when my children were small I was too poor to own a car. I used a bike, and the habit has stuck. I still use the bike for shopping, and a combination of bike and public transport to go to work. I make time in a busy life to fit these things in.
A few years ago this behaviour might have seemed eccentric. But the recent Stern report suggests that even ordinary, everyday things like driving to work and using supermarkets are contributing to global warming.
Topics such as climate change, carbon footprints and garbage mountains are daily news. Early years practitioners, no less than any other responsible citizens, have to take a moral stance about these issues and think how their practices might have to change.
Children need to understand about the precariousness of our planet and the vulnerability of many of those who live on it. How about a national prize for the 'greenest' nursery - the fewest staff and children arriving by car, the least use of plastic wrapping and disposable nappies, the most home-grown food, the most socially responsible purchasing, as well as the most energy efficient building - all this reflected in activities with the children?
Green living is not uneconomic or unrealistic; it is our necessary future.
Our children won't thank us for doing otherwise.
Helen Penn is professor of early childhood studies at the University of East London