Piglet heads are fractionally off-center on their body, with the left side of the head clipping into the body and the right side fully visible.
Puppy heads, by contrast, are perfectly centered, which causes z-fighting where their heads and bodies overlap when looking forward.
Since both baby mobs' heads are the same widths as their respective bodies, both heads have the potential for heavy z-fighting and clipping issues, especially if/when the piglet's head is properly centered on the body.
A fractional inflation of both models' head elements (even by a factor of as low as .02) would remedy both issues without noticeable changes in pixel consistency or pixel density on the models. Inflation is already used for sheep wool elements to use the same UV-mapping as their underlayers, so inflation would not be wholly out-of-place as a fix here. Screenshots attached showcasing off-center Piglet heads and z-fighting on Puppies' shoulders.
I have edited the title to focus on the Pig issue, as the Wolf issue is already covered here: MC-305492