It's an interesting passage that is hard to understand. Who is Jesus saying that Peter and himself are sons of?
The king does not collect taxes from his own sons, but from strangers. So the sons are exempt. Sons of whom? The king. That would seem to indicate that sons of the earthly king do not have to pay taxes to the earthly king, and sons of God do not have to pay taxes to God. Which is not what Jesus is saying. I struggle to follow the argument logically to the conclusion that Jesus reaches.