As a bounty hunter and an assassin, Zero has never been fond with kids because of their attitude against him. Last time he's fond with them, the kids mentions him about the war with Zukin and called him a fake veteran. That was the last time he's fond with kids and begins his career as a bounty hunter.

Zero:  Beside, I did something to the kids and their parents.

Anonymous:  What did you do?

Zero:  Arrest them for misdemeanor and battery against their neighbor.