Six year old Michaela and four year old Carrie stayed with us for the evening yesterday. Their parents were out for an event, and we had the pleasure of our granddaughters' company.
Michele cooked lasagna for dinner. She served it with toasted, rustic french bread. Michaela noticed the large air pockets in the slice she was eating. I told her the bubbles were caused by yeast.
"What's yeast, Grampa?" Michele urged me.
I explained that yeast were tiny, tiny animals, and when you made bread you started by taking flour and water and...here I looked to see if I hadn't passed the girls' attention spans...and then you added yeast, which looks like a dry powder. The yeast wake up in the wet dough and start eating the sugar....still paying attention?...then the yeast burps and farts carbon dioxide, which makes the bubbles in the bread.
I remembered that the girls came from a household that calls flatulence, 'bustering'.
"So when you are eating bread, you are eating yeast busters."
Michaela smiled and ate the bread without interruption.
By 
Well, now I know where to direct my kids when they continue to ask me the "WHY" questions. I usually can give a nice explanation like, Yeast makes the dough rise. But anything more scientific than that... I guess I'm going to be shoving my kids your direction.
I love this story, by the way.