How can you explain commodities , futures and the link to farming to a child?

[Raisinable]

I've tried a lot of websites and books but none of them break it down fully for someone just getting familiar with this. I basically understand the idea of hedging, but I get a bit lost when people talk about spreads and basis and most of all, I don't understand the link between physical commodities and all these bits of paper that are apparently traded on futures exchanges.