The punishment for running over Tabby or Fido is greater than drowning a baby in a toilet.
There is no punishment for accidentally running over Tabby or Fido, nor for humanely euthanizing Tabby or Fido (either at the vet, or with a clean close-range shot to the head). Quick killing of newborns is generally viewed as a panic reaction, especially when, as usual, it's by a very young mother who has good reason to fear abuse from a parent if the baby is discovered. Such cases virtually always draw at least a short prison term or a psych hospital term. The girl who drowned her newborn in a toilet at a high school prom a few years back, and then went right back to dancing, spent at least a couple of years in prison, as I recals, with several years of parole/probation afterwards. Repeated infliction of severe pain on a newborn, whether or not resulting in its death, or serious neglect of a newborn (such as not feeding it), will result in a signficantly longer prison term. Sadly, what those deliberate heinous acts do NOT result in, is sterilization of the perpetrator before release. As a result, most of the severe child abuse cases we hear about are "not the first time" cases.