Create time-lapse gif centering point of interest
You don't necessary need to make it the center of the image but always appear at the exact same point in the frame. The center is usually an easy referencing point for that purpose, so why not use that. 

Obviously the easiest would be to make the photographs in a way that they don't need postpcessing. If this chance has passed already, you can get a (free) image editing software like the "gimp" and move &amp; scale alle pictures in a way that they have approx the same size and center.

BTW good luck with the baby, ours is almost 3 months already and it has been quite some experience so far.