Idea 02 - The monster that eats shadows -

Narrative (kid's voice): I used to sleep with lights on because I believed that there were monsters... till one night, I woke up and I actually saw monsters... They were eating shadows... The desks, chairs started to fly away as they lost their shadows. I turned the lights off so the monsters couldn't find my shadow... Today, I still believe that there are monsters and that's why I sleep with lights off.