He could be messing around but if it turns out to be serious you may wanna call a priest and your local Catholic church.
My 8 year old son sees what he calls, shadow people. Usually he will see it while passing by a room, but today he seen one "running". what is it, what should I do, also what should I tell him?
Well, you don't know what's going on inside his head. He could be playing around, or perhaps he has special abilities. Whatever it is, don't worry. Tell him it's cool, make him feel good about it.