porphyrogenitusMises was a Utilitarian, so it’s hard to say. Actually, it’s hard to say where many people would come down on this question until they’ve taken their position and explained how it connects to their general world view.
I mean, Rothbard was a Natural Law theorist, and many (but by no means all) adherents to Natural Law are pro-life, but Rothbard was not.
But be that as it may; what matters most IMO isn’t where they came out on this specific issue, but what you think is the correct position, even if that position is based on accepting their own general principles. I happen to think Rothbard went badly wrong on the whole issue of children (much less the unborn). A fair number of “Rothbardians” also think he did. Even great thinkers are not always correct (Mises utilitarianism I find unsatisfying, to say the least, and I think Rothbard was on firmer ground in taking a Natural Law approach).
But it’s not really possible to ascribe views on this subject to anyone who didn’t explicitly take them, themselves. (It may be that Mises did express himself on the issue of abortion et al; I can hardly claim complete familiarity with all of his statements, alas).