Previous kids' talks have used the idea of layers of bricks, likening the apostles to the first layer, and each generation of Christians built on top of them. I have also used the idea of Cephas' renaming to Peter, solid on which you can stand. We also have a boulder out the front of the church with a plaque commemorating the opening of the new Holy Innocents back in the 90s. The plaque is on rock because it is so solid and will last. Like God.