Rothbard defined liberty as self-ownership: each individual has himself as his property. From this, he deduced that the product of an individual's labor, being partially derived from the individual's body, is also the individual's property and that an individual property right in the product of his labor cannot be violated without also violating his self-ownership. Thus, his entire philosophy rests upon the concept of "self-ownership". I perceive some immediate problems with this concept that I shall attempt to resolve. The first one is that it allows someone to sell himself into indefinite absolute slavery, like he has the right to sell any other property. If we deny the legitimacy of the institution of slavery, we must accept that the "self" is not exactly "property" in the same sense as land or food. Yet, why this distinction is made is not very clear. The concept of self-ownership leads to, as its immediate consequence, property in the product of one's labor. The second issue with the concept of self-ownership is this: who owns a baby? The mother, whose product of labor the baby is? Or the baby himself, since all individuals own themselves? This is not immediately clear from the concept of self-ownership. I'll address both these issues.
To understand the concept of liberty it is essential to break down human existence into the physical aspect (the human body) and the non-physical aspect (the human agency; moral, intellectual and emotional). Human agency is quite simply the faculty of purposeful behavior. No matter whether such agency can exist independently of the physical body or not, it is, as a concept, distinct from the physical body. The fundamental principle of liberty is that human agency has the right to materially express itself unobstructed, but within the same right of others. This immediately necessitates the ownership of the human body by the agency, yet the agency itself is not owned by anyone, not even itself. From the ownership of human body one can derive ownership of the products of one's labor, i.e., property rights. Yet, the fundamental distinction here is that property rights emerge from the more fundamental right to liberty, and not vice-versa. This immediately solves our first problem: a person cannot sell himself into slavery because in doing so he would sell, along with the rest of his body, the very faculty of decision-making. This would not be a legitimate transaction since it would be in violation of liberty.
Reproductive conception is not invasion on part of the child to be born, since being conceived is not a conscious act, let alone voluntary. On the contrary, since the body of a child is caused to be conceived in a naturally dependent position by his parents without his consent, the parents owe restitution to the child. The child is entitled to a minimum level of care by the parents sufficient to bring the child out of the natural state of dependency. Furthermore, the parents shall be the trustees, but not owners, of the child until he comes of age. As trustees of their children, parents shall be liable to pay compensation for any acts of invasion perpetrated by a child. Parents shall have a reasonable amount of say in the private life of their child, to the extent it is intended to prevent or mitigate harm for the child or preventing the child from violating the rights of others. When the child achieves reproductive maturity, since the child can reproduce and can thus be expected, according to the laws of nature, to take care of children of his own, he most certainly can be expected to take up responsibility of his own life. Thus, the child is not to be considered biologically dependent upon the parents beyond the common age of reproductive maturity, and neither do the parents owe the aforementioned duty of care beyond this point.