While I was trying to put the Little N down, we had the conversation below:
N: I am scared
M: What are you scared about?
N: the monsters
M: Do not worry, mommy and daddy are very mean, we have scared the monsters away, they are going to different houses now.
N: But what if the other parents scare them away too?
M: Then they will scare each others
N: What if they do not want to scare each other
M: Then they will play with each other.
N: What if they do not want to play with each other?
M: Then they will go to the other planet, because earth is not fun for them anymore...

N: oh, they will just fly away? ....