I know this is not cut and dry, but I teach my son about carbon/nitrogen through life and death:

Green living grass = nitrogen
Green living leaves = nitrogen
Brown leaves falling off the tree = carbon

After this quick lesson, he asked, "what am I?"

I said, "don't sit in the leaves for too long or I'll be adding you to the garden."

He was more interested in the chemical reaction that happens to cause the heat.

Will you be able to "show" the kids a working compost pile, or will this be in a classroom environment?

My son is 9 and will enter the 4th grade next school year.

Saucy

I'm not certain you can get much simpler mnemonics than greens and browns. As has been discussed at length in SCM they are merely truisms, but they are a starting point. That is to say any plant material harvested green remains a green even when dried out, and any plant material harvested after it's natural death is a brown wet or dry. There are interesting exceptions such as coffee grounds that are colored brown but are a compost green, and paper that can be many colors but is a compost brown.

Working with the children in our neighborhood I've found the boys most fascinated by it. The girls will work the garden but have close to zero desire to be near the compost. OTOH the boys are real slackers in the garden and revel in turning the compost. They all like to watch the temp probe get inserted and see the gauge climb up to 100F or more. They are pretty comfortable with technology and the numbered dial is quite familiar to them. They get it. They just don't understand the biology behind it. Setting up some kind of demonstration pile (With probe!) gets my vote.

I've been doing some thinking. I'm not going to use the words carbon and nitrogen. I'll just tell them you need to add some brown stuff and green stuff and then expain what things are brown and and what things are green. I found it difficult teaching kids because I get way to technical. They don't care about the specificities. They just want to have fun. So I guess what I really need to know is how to make this lesson plan fun and interesting for them so they don't lose their attention.
Yes, I can have a living compost pile, at least at most of the schools. Sometimes I teach in the classroom and in those instances I would have to put the compost in some sort of container.
Thanks for your responses. I would appreciate any additional ones.

Or there's this, which I think is a great prop for kids. I'm going to make one for the grandkids this Summer. Worms are the original composters, after all. :-)

http://www.diynet.com/DIY/article/0,2058,2275,00.html

Here is a link that might be useful: worm farm

You want to impress upon them that layering greens and browns are important.

Bring a large glass pyrex baking dish.

Layer the bottom with graham crackers (brown)

smear on pistachio pudding (green)

top with slivered almonds (brown)

almonds are very thin, more brown needed,

but before you add more browns show that it attracts worms and bugs. Put in some gummi worms.

Add another layer of graham crackers.(brown)

Add more pistachio pudding (green)

Sprinkle with chocolate chips (brown)

Sprinkle with green tinted coconut (green)

Spoon it out into cups, let the kids eat it up for a fun treat.

You could bring in two props, a can filled with finished compost and another filled with grass clippings, and declare them both filled with dirt. Kids love non-sequiturs. Their brains have been forming all kinds of associations for years and now someone presents an odd puzzle that somewhat contradicts what they know.

You used an important phrase earlier: living pile. That would be a good non-sequitor later in the lessons. Reveal soil to be another atmosphere filled with life. There are creatures that live in a sea of water, we live in a sea of air, and there are still others that live in a sea of dirt.

I like Trudi's idea, but don't use nuts, please! Many schools have a no nut policy. And please check for other allergies in the class too. Nothing is as disheartening to a kid as being left out. (I know that first hand)

The great thing about worms is their poo. Kids love learning about poo! They may say "Yew, gross!" but they won't forget the lesson.

I recently taught 18 4-year-olds how to compost!

Our making dirt experiment took place on two days. I brought in apples for snack. We threw all the scraps into a big plastic bucket I'd brought for the purpose. The kids loved feeding the compost monster! I pointed out the airholes I had predrilled. We'd made a mascot puppet, Wormy. At playground time, we gathered leaves, mulch, etc. We also tossed in (accidentally, but it worked out great!) two plastic cups, plastic spoons, and some paper napkins. I added some nice healthy dirt from my garden at home. Then we added water. I read a great book entitled _Compost_ to them. It follows a family composting in a larger scale throughout the year.

I took the bucket (a recycled bird feed bucket) home. The handle made it super easy to turn. I checked for moistness, and broke up the apples with a hoe. For older kids, I'd have them chop their scraps; the four-year-olds just tossed things in, so I had to help the pile along a bit.

Six weeks later, I revisited the school. The kids loved discovering the rich black compost they'd made. They spooned it into containers, spilled it, smelled it. They also discovered that plastic doesn't turn nicely into dirt! I sent them home with their compost, little plants to pot up, and instructions to the parents for making a pot for the plants out of recycled materials.

Lessons: decomposition, microbes, plant cycles, browns/greens, recycling.

I've also heard of people doing this in large terra cotta pots, and individual plastic zipper bags. For the zipper bags, each kid gets two. One bag gets aired out every couple of days; one doesn't. Takes a week or two. Then they open them (outside!) and figure out which one stinks! THAT would show the importance of circulation, wouldn't it? EEEYEW!

Im sure Im to late for this but I took circles of different color fabric and wrote the different layer names on them and we took turns layering them