Sorry I haven't posted a children's sermon for the last two weeks - I wasn't preaching! So, for this Sunday, here's my plan.
I'm focusing on the 'yeast' part of the parable, and I am going to bring in two cakes - one made without any baking soda/rising agents, and one made with. I will show them the flatter cake, and ask the children what is wrong with it. I'll talk about how even though it is such a small amount of the recipe, a bad-tasting, unexciting ingredient, it is totally essential to the cake. I'll tie that in to the kingdom of God, and to our own essential and important role in that kingdom.
Not a perfect comparison. But it will do :)