Isn't it amazing how many different answers we can get to what was supposed to be a simple question?
I guess the parameters placed on the thread early on made for some confusion. In any event, they all have some validity. As we often say in stamp collecting, there are often no right or wrong answers ... so in order to summarize, let me present the following:
A. If we accept the criteria that the person need not be named as such on a stamp, then the Baby Jesus would be the correct answer.
B. If we accept the criteria that the person MUST be named on the stamp, then the Virginia Dare stamp would be the correct answer (as she was pictured as an infant.)
C. If we accept the criteria that the person MUST have been famous or well known to the general public in some way or another, then it seems the 17-year-old Ritchie Valens stamp may be the correct answer.
I'm not aware of any pregnant women depicted on US stamps.
The previous comment about Egyptian stamps may be true, but does not apply to US postage stamps.
Finally, while this may not be the youngest person, if we are going to start looking at generic US stamps where an infant appears on a stamp, but need not be named, this one may be in the running, as well (although there may be others I haven't thought of):
