There are props for and roles for all of the children in the class. One gets to be the farmer who wears the hat and stirs all of the ingredients together to make compost.  Some of the kids are brown or green leaves while others are bacteria, mushrooms, worms, beetles or centipedes.  They all do their part to make the compost.  At the end, they all become part of the compost and the farmer "scatters" them all around the garden (classroom). 

There is a flip chart which takes you through the skit. 

With younger children just acting out the skit is enough.  With older kids, add a discussion of food chains and energy pyramids

Master Gardener-1 (You will need 2 Master Gardeners if there are 25 students) 
Brown Leaves-5 
Green Leaves-5 
Bacteria-3, Mushrooms-3 (First level consumers) 
Worms-3, Beetle-1 (Second level consumers) 
Centepedes-2, Ant-1 (Third level consumers) 

Directions
1.) If you have enough adults have them form a circle and be the actual compost bin.  You can also have 4-6 children hold hands to form a circular bin too.  If so, decrease the roles with the most participants by one. 
2.) Master Gardener adds leaves and grass to his/her compost pile. 
3.) Master Gardener adds O2 to the bin by stirring with the pitchfork.  The browns and greens wiggle. 
4.) Maser Gardener adds H2O to the bin with a watering can and browns and greens slurp.  Master Gardener takes the temperature of the pile. 
5.) Conditions are perfect so bacteria, mushrooms, and worms eat the browns and greens. Browns and greens decompose by curling up. 
6.) Worms (or Springtails) and beetles eat the bacteria and mushrooms.  They curl up. 
7.) Centipedes and ants eat the worms (or springtails) and beetle. 

After the last step go over the roles with the students.  ASK the students what could happen to the centipede and ant.  Could a bird eat them?  Could any of the worms or the beetle be eaten by something outside the compost bin?  Explain that the food chain doesn't end after the ant and centipede.  Besides getting eaten by an animal outside the bin, they can also die and then become food for the bacteria and fungi.  So a compost pile is an example of how nature works in cycles and reuses everything.  Point out that we need to live our lives the same way, and that recycling is one way of doing that.

With older children discuss the Food Chain
For older students you can go into why there are fewer organisms at the top of the food chain.  Explain that when another organism eats an organism, not all of the energy inside the eaten organism gets transferred to the other (2nd law of thermodynamics).  Only about 10% of the energy gets transferred to the next organism, the rest of the energy gets converted to heat. 

  Organism         Energy Available to Next Organism 

  Leaves & Grass  100% 
  Bacteria & Fungi  10% 
  Worms & Beetle  1% 
  Centipedes & Ant  .1% 

To prove this idea ask them how hot their compost pile was?  At each energy transfer heat is produced. 

Animals who eat plants are called herbivores. They are considered consumers and are next in the food chain. 

Animals who eat other animals are called carnivores. They also considered consumers and are a link farther along on the food chain since they need the herbivores for their food. 

Animals and people who eat both animals and plants are called omnivores, and they are also part of the consumer piece of the ecosystem. 

Finally, the last part of the ecosystem is the decomposers. These are the living things which feed off dead plants and animals and reduce their remains to minerals and gases again. Examples are fungi, like mushrooms, and bacteria.