Bed Time Troubles

I got a rare peak into Mason and Myles' secret bedtime routine last night. After Marshall was done reading them stories I was resting on Myles' bed. Marshall tucked them in, turned off the light, and shut the door. A second later Myles says "Mason, are they gone?" and Mason answers "yep they are gone." They both jumped out of bed and started dancing and jumping around the room! I said "excuse me!" and they both jumped back to bed and exploded in giggles saying "we didn't know you were still here." I asked and they said they do this every night. About 20 minutes after I left Myles came downstairs crying and said that Mason told him there was a monster in their room and described it in vivid detail. It was pink with pointy teeth and long claws and crawled along the floor eating little boys. After questioning Myles a little more he said that every night Mason tells Myles about monsters and then Mason falls right asleep but Myles is up for hours worrying about it. This morning I warned Mason not to tell Myles anymore scary stories before bed.