I happened to have a silicone mould with people shapes that I'd picked up at the pound shop, though really any kind of mould would be fine. Silicone worked with no mess, but I'm probably not ever going to be using it for baking again!
Break or cut crayons into small pieces and get children to arrange various colours in the moulds. Don't fill right to the top or you may have spillage!.
Talk about the different colours representing different skills and gifts that different people within the church or within the group have. Children might choose specific colours to represent what they know of certain people.
Now put the mould into a preheated oven at about 200 degrees (e.g.quite hot!) and bake for anything between 5 and 8 minutes. Keep an eye on the melting and when it looks as though everything has melted with no lumps, take out the mould and let it cool.
When the mould has cooled down, pop the melts out!
Each child can take their melt and see how the colours that were once individual have now formed into one unit and can not be separated without causing serious damage. Every colour can still be seen, but it is strongly linked to the other colours.
Talk about the body of Christ (1 Corinthians 12: 12-31) and how we come with our different gifts to make up the whole body. The individual parts can all be seen, but each part is equally as important to making up the family of God.