Just found a great website where you can create environmental awareness among your kids. You do this by calculating their carbon footprint (carbon emissions) and finding ways to reduce them.
It called the Carbonator (carbon + calculator)) and you can find it on the RSA Carbon Control site.
It might be useful for adults as well.
Before you can use the carbonator, you have to register with the site first. They also have a list of some great projects that you kids can take up.