Just go to sleep!

I have been having to listen to my 21 month old call "mama, mama, mama" or "dada, dada, dada" for 20 minutes before he goes to sleep for about 2 weeks now. Tonight, before putting him in bed, I had this conversation with him: "Zealand. I love you. Daddy loves you. But when we put you in your bed, it is sleeping time. Tonight, when we put you in your bed, I want you to cuddle with Blue, close your eyes and go to sleep. No calling for mom. No calling for dad. You need to go to sleep."

We walked out of the room and closed the door.
Its been quiet for 38 minutes and counting. Why didn't I have that conversation way earlier???