Here's two of my ideas:
1. "Play Time"
In a bright, happy daycare center, there are two little boys drawing as they sit on the floor. The one boy draws a monster, and the other boy draws a robot hitting the monster. The first boy gets angry, and draws a new picture of something more menacing. This continues until two of the boys' drawings come to life and start fighting right there in the daycare, destroying everything. Then, in the middle of the action, we cut back to the two angry boys sitting across from each other on the floor. One boy has his arm raised with a small wood block in his hand. He throws it and pegs the other boy in the forehead. Just as the boy begins to cry, we cut to credits.
2. "Sticks and Stones"
Scene opens on a cliff, where there's a small little sprig of a tree. We see that it's alive when its eyes open. It has little twiggy arms and legs. It gets knocked loose, falls, and lands on a large boulder. Rocks fall down from the cliff, and the twig jumps off the boulder to dodge them. Turns out, the boulder is alive too, and he's pissed that the twig woke him up. Boulder chases twig through the forest in an exciting chase scene. Boulder trips and crumbles. Twig timidly approaches boulder. Camera fades. New scene opens on closeup of mossy rocks, which turn out to be the boulder with a large tree grown on top of it, which is... you guess it, our little twig.