You should never have acknowledged there being monkeys in the room by way of pretending to clean them out. He should have been told that monkeys live in the zoo and they play all night and the zookeepers take care of them. Something like that. It's never too early to teach children what's real and what's not. What's imaginary and what exists.
My friend tried this tactic and it worked beautifully. She very patiently put the child to bed, and held her hand until she was asleep. She did this for a few nights. Then she sat within arms reach with the child in her bed until she was asleep. Later, she moved farther away, but still in her room. Later, she sat outside the child's door until the child was asleep. Finally, she said she would be within earshot, so if she needed her mom, she could call. The child just needed some security that took some patience to create. I don't know if I could have this patience, but it worked for my friend. Good luck and God bless.