Tell the kids you are making brownies today.  Put your apron on and pull out your bowls and spoons.  Have a child read the recipe step by step and when it comes to adding the cocoa make a big deal out of how you forgot to bring the cocoa and look around and see that there is some dirt in the potted plant (which you brought) and use the dirt and add it to the ingredients in your bowl.  The kids will really be into it and tell you no but tell them it's okay dirt is brown just like cocoa and it shouldn't make too much of a difference in the recipe.  When adding the sugar you just accidentally forgot to bring enough so use your can of salt and say it's okay because salt is one of the ingredients in the recipe and your just putting in extra since your sugar has run out.  You can leave things out also. I put the batter in a pan and everything and put it into a "microwave" behind the podium. We then sang a few songs and when the timer went off I pulled out a cooked batch of brownies and asked anyone if they wanted to try some of the brownies that we had just made.  Of course most kids said no but there were a few who thought they would give it a try.  For these kids I had already prepared a very salty creation before my lesson and I had added it to the pan.  They got a big surprise when tasting the salty yucky brownies.  I asked them to describe the taste and did they feel let down after thinking they were going to get good brownies.  Christ showed the apostles certain ways to do things in his church ie. baptism by immersion, etc.. When the apostles died the people started to change things that did not seem like such a big deal at the time but changed the church from what it was suppose to be.  I still have kids commenting about that lesson even after a year.