You begin to wonder how long it would take to freakout the kid if you continued to grow the puppy. You think of the puppy growing bigger and bigger, and watch as the kid continues to play with the puppy. The puppy continues to grow, and its footsteps are causing tremors. You stop growing the puppy once its paws are twice the height of the boy.
The impact of its paws on the ground cause earthquakes that leave huge dents in the ground. The puppy barks, and that is what gets the kid. The kid is suddenly filled with fear when the deep, powerful bark comes from the puppy. The kid begins to cry, and runs in the house, and the puppy tries to go after it, but can't manage to get in the house at all, given its paw alone could destroy the entire house.
You are amused by this. You like how this turned out, so you find something else to mess with.