Brian, I'd say it would be part of the sentencing procedure handed down by the court. Just as people are banned for life for certain driving offences, imprisoned for life for certain types of murder, people who have treated their children in this manner will forfeit the right to produce more. If a 'stranger' paedophile rapes a 9 y.o. child, the world is filled with revulsion and he (as it usually is) is banged away for years, but can be free to be released after time served.
I'd argue that there's no such thing as 'time served' for his tiny victims, though, and when the horror has been perpetrated upon them by the people who should be most protective of them, their own parents (male and/or female), these people have shown themselves unfit to care for their own procreations. Not because they're disabled, not because they're mentally unfit, not because they're of a certain race, religion, whatever, but because they're completely out of control and have proved themselves unfit to parent. They can go to jail, as punishment, sure, and like the stranger paedo they're out in a while, but, unlike the stranger paedo, their object of torment will be out of their reach and no more can be made to replace him or her.
I don't see this as being enacted in the sort of case where someone's momentarily lost their rag with a bolshie kid and belted it. We're looking at years of systematic and KNOWING violation of YOUR OWN CHILD. I think the least one can do for the surviving kids is for them to know Mommy and Daddy won't be focussing their perversions on a replacement batch in future.
I don't think all humans have an automatic right to wanton reproduction, no, to be honest, I don't. It's got nothing to do with master races, it's got everything to do with ensuring that, as much as possible, children will come into as welcoming and caring an environment as possible. I can't imagine why anyone would allow lives of degradation and cruelty to be just the luck of the draw for them, whether it's through bottomless poverty or predatory parenting, because of some over-intellectualized concern based on a misunderstanding of eugenics, itself the subject of vile abuse by the Nazis in a perversion of its' original intent, which is to genetically modify OUT the causes of crippling diseases and genes which pretty much ensure a short, agonizing life for many thousands of babies worldwide. I know the Nazis sterilized those they considered unfit to breed, as part of their master race programme, which has nothing to do with ensuring criminal parents are not permitted the further joy of parenthood in order to violate their children.
The evil of the Nazi abuse of genetics (including the forced sterilizations) paralyzed what would have been a continuing programme of research, working towards healthier babies with an expected decent life span. This was hijacked, as we know, and sadly there are thousands of parents today who have to watch their babies die, when gene replacement may have saved their lives. Again, nothing about master races in this, just what is plain good sense, from the child's view, and from the economic standpoint.
Unfortunately, mention 'genes' and you pretty much get the sort of reaction you've given, which is what kept the influence of Nazism going over the past 50-odd years, by denying rational examination of genetic modification and advancing the cause of, especially, paediatric health. It's the reaction which means parents have to take lengthy, financially and mentally exhausting cases for review by the court of Human Rights in order to be allowed to produce another baby to help (through its' genes) its' sibling survive. It's honestly time we all grew up a bit about the issue, especially as there are already in place plenty of edicts to prevent it falling into the abuses you mention.