There are lots of resources that explain the basics of composting so someone completely new to the idea, or your children, can learn about recycling food scraps to create fertilizer.
Check out this compost recipe: http://www.ecy.wa.gov/programs/swfa/kidspage/compost.html
This explanation of the value of composting: http://www.benefits-of-recycling.com/compostingforkids.html