Perhaps you've seen the movie Lilo and Stitch.
Perhaps you remember the scene in which Stitch is frustrated because he is nowhere near a large city so he creates his own miniature city with Lilo's toys, and then proceeds to crush and destroy everything as if he's a 40 foot beast.
Now hold that image in your mind and imagine a young baby, innocent of face. She has just recently begun walking, so her gait is still unsteady. She sees a small rug on the floor, with pictures of roads and buildings on it, something that Middle Child enjoys driving his cars upon.
Baby Child homes in on this rug. Several grunts escape her lips. She lumbers forward -- stomp! stomp! stomp! She growls like a primeval creature and begins to crush and destroy everything in her path. Smash! Kick! Grrrrrr! She aims carefully, and sits squarely on Middle Child's hands and/or head. Middle Child shrieks and runs away, in fear of his life.
Satisfied with her efforts, she climbs into my lap for a cuddle.
I have created a monster, and she isn't even 11 months old yet.