It's pretty interesting, really. Mammals in general have a strong instinct to recognize and protect the traits that characterize infants (disproportionately large head/eyes, high-pitched vocalization, etc), which is where we get our concept of "cute", and why cats and dogs will sometimes be extremely tolerant and protective of human children who are much bigger than they are. Occasionally, the instinct is a little too strong and overrides survival traits like "eat that delicious baby." It happens often enough to be well-documented, but it's really not the norm.
