You need a clear glass, some instant coffee powder, water, and a bucket
You hold up the clear glass filled with water so everyone can see it. Tell them it represents How God wants our spirit/heart to be clear and pure and healthy. But things happen though out our lives that hurt that. Then add a small amount of instant coffee powder to the glass which will make the water a little darker, that represents our spirit/heart being damaged like when some one makes fun of you. Give many examples like that and add coffee after each example making the water darker and darker like when you are wrongfully accused or when you were picked last in baseball, etc. Now you see a damaged spirit/heart, but when you have God he takes all that dark and nasty damage in our spirit/heartaway, then add water to the glass until it turns clear again. This was a pretty powerful demonstration that worked for us and I hope to pass it on.