If you end up with a child you don't want, don't sweat! You can let him or her starve to death.
From the linked article:
"But the parent should have the legal right not to feed the child, i.e., to allow it to die.[2] The law, therefore, may not properly compel the parent to feed a child or to keep it alive."
I know you're being facetious, but you're already not compelled to feed a child, you can just drop him/her off at a police station or hospital.
Not that I don't think that article is full of crap. If we're going to apply property-based libertarian principles to the letter, then we need to talk about the months of imprisonment in a dark and confined area that the mother imposes on the child :P
I think you must have read the quoted passage but not internalised it, because it does actually say that there should be no law against killing your kid.
No, it does not say that. It says that you should not be compelled to feed your kid. If you read the passage in context, you'll find Rothbard is explicit that you cannot kill the kid, nor stop the kid from leaving if the kid is not happy with the support you are providing.
Of course as a practical matter, if the kid is young enough, or you live sufficiently far from other people, the kid cannot exercise its right to leave, and so effectively you can kill it by not providing food.
From the linked article:
"But the parent should have the legal right not to feed the child, i.e., to allow it to die.[2] The law, therefore, may not properly compel the parent to feed a child or to keep it alive."