Well, it's obvious, so obvious in fact, that it's incredible that no one thought of this. Go to sleep with the doors closed and your flashlight on. They can't get in that way and it would've worked in FnaF 4, IF YOU COULD SLEEP.
I would say "Wow. Its the demon under my bed even thought I have a bunk bed.. Wait- You live in my closet dont you? yup. Oh wait its coming closer-" *Screams and throws a glow stick at its head*