Guardianship (tutela) was a legal institution developed to protect children whose paterfamilias had died before they were of an age to manage their own property (property which, presumably, they had inherited from him).
Normally, such children would have been born during their father's lifetime and within a legitimate marriage, and would have been recognized by their father as his legal heirs before he died.
But what of children who, though conceived within legitimate marriage, had not been born until after their father had died? In such a situation, not inherited property was at stake, but also questions of paternity and legitimacy, upon which the transfer of paternal property depended.Children conceived in a legitimate marriage were their father's heirs if he died intestate. An unborn child had to be explicitly disinherited in their father's will [Thomas 1986, 214]. If the father had left a will but had not included a posthumous child (called a postumus), presumably because he had not been aware of his wife's pregnancy, proof of the child's existence would break the will [see D.40.4.29 in Chapter 4, Part I.E.2]. In the eyes of property-conscious Romans, it was essential to ensure both the paternity and the survival of such children yet to be born. As with the divorcee who claimed to be pregnant by her exhusband [Chapter 4, Part I.E.2], attention centered on the widow who had become pregnant before her husband's death but who did not give birth until afterwards.