Wrist would break?

Perhaps. Although one punch to Superman's chest usually doesn't break a wrist. It takes two or three. :P

Well..Most people who punch Superman aren't children though..Hrm..I'unno. It probably would break his wrist, now that I think about it. Unless it wasn't a full on "I'm-trying-to-knock-you-out" punch, as Demon said. Then his hand would just hurt like hell. xD