Thanks, Maiden Stone.
From all the responses I have had to my enquiry, there seem to be a number of possible explanations, some more remote than others.
I guess I have to make a tentative decision towards the one that seems to me most likely, while keeping the other possible explanations open.
The fact that the Catholic Church reserves baptism for the living seems to rule out stillbirth, although Gaffy's point that baptism could be carried out if the child was "at risk of imminent death, including cases of doubt (ie. uncertain if alive, but where there might be the slightest chance)." Further, I note the high infant mortality around that time in Ireland - something over 20% - so I am leaning towards the possibility that the child's death was imminent and baptism was given with no regard for recording the niceties of a name and gender. The fact that this child did not come up in any later records leads me towards that explanation rather than the minister forgetting the child's name, or the parents not having a name chosen.
Thank you everyone for your help.
I am satisfied to close this post now.