Let's go back in time, back to the dinosaurs. Because they were awesome, like chimpanzees

Chimps are actually really cool. They are the species closest to humans in both development and actual practice. But more than that, they are cannibals. Sometimes.

There was a documented period where these two chimps, mother and daughter, were killing baby chimps and eating them. Really weird and kind of sad, but true. No one was entirely certain why that happened, but as soon as one of the chimps had her own child, they stopped.

Dolphins are weird like that also. Male dolphins will kill a mother's young in order to breed her themselves. Don't think they eat the young though.

But infanticide is definitely a thing in the animal kingdom. Not legal in the human subsection of that kingdom though.