Yang Kai should never have children. He would be the worst father. He brought that evil dude to the world tree. Even a water flea would have enough wits to know Wu Kuang would try to devour the world tree. Because that's what he does. But of course Yang Kai has less wits than a water flea, so maybe I'm being unfair here. Still, what did he do afterwards? He told Wu Kuang not to act recklessly. Yeah. If Yang Kai had a child, the child would become a spoiled cultivator and one day might decide to destroy a random cultivation world with a billion inhabitants. Yang Kai would just tell his kid "not to act recklessly". He should never have children, despite sporting a large harem. Never.