Ask your son what color the dog is and what color it's eyes are.
If he says the dog is black with red eyes, you have a serious problem...
For now, grab salt, sage or basil, and pepper from your kitchen cabinet. Mix them together (pray as you mix) and make a line with the mix around your bed, finish the circle at the wall lightly if the bed is near the wall (doesn't need to be perfect). It will vacuum right up in the morning.
Chant "By this circle I cast, no harm shall pass"
For your son you can add "by this circle I cast, no scary dogs can pass" so he understands.
This creates a physical boundary. Tell your son the mixture will protect him. Sprinkle a little on his favorite stuffed animal and tell him it will protect him too.
I want to know the colors tho. That's just a temporary thing for tonight