Doubt About Mahabharata

In a remote village of India, once Masterji is teaching the Mahabharat katha to class 6 students. He is at the Krishna janma part of it.

Masterji : Kansa heard the akashwani that his sisters 8th child is going to kill him. He was furious. He ordered to put Vasudev and Devki behind the bars. First son is born, and kansa kills him by poisoning Second one is born n Kansa throws him off the mountain peak. Third one is born

Ramu : I have a doubt (sounding nervous and confused).

Masterji : Ramu bete, whole India does not have doubt in Mahabharata then how come you have one?

Ramu : Masterji, if Kansa knew that Devakis 8th child was going to Kill him, Why the hell did he put Vasudev and Devaki in the same cell?

Masterji fainted.