I've heard people say it too, but never when there hasn't been a valid reason from the animals pov. Plus animals don't have the same type of empathy and understanding as humans do, so it doesn't have the same malicious intent.
Eg the cat that tortures a small animal. Naturally, that's how they teach their young to hunt, it's for a survival purpose. And as many domestic cats don't get further along the maturity route than that they continue to do it as adults. Different to a cat hunting for food that wants to expend the least energy and take the least risk to procure food. Neither is malicious or aware they are inflicting torture. And entirely different to eg the likes of Ian Huntley.
I suppose the comparison is a toddler deliberately hurting another child, physically or by snatching and breaking their favourite toy in a tantrum, there's no intent or understanding as there is with an adult human.
Plus I think the human race as a whole is pretty shit at communicating beyond the verbal. So eg the dog that bites a child out of the blue has usually been communicating that likelihood for ages but nobody read the body language.
Barring psychopaths, I don't think anyone that says they hate babies and children mean it in the true sense. More they hate the behaviour, work, noise etc. Eg if a friend brings a baby or toddler round, I find them cute, enjoy interacting etc. But would privately tell dp that I'd hate to have more and be back at that stage 24/7. Whereas if they bring a puppy dp will be listing all the reasons another wouldn't be practical before they've left. If I didn't already have dc and therefore didn't entirely understand that stinking nappies and constant supervision come with a billion positives when it's your own, then I could imagine saying I hated them if my experience was only badly parented dc, even though I'd be using the word incorrectly. Eg as I hate shopping or soggy veg.
I suppose it's babies rather than children because they are more noticeable. So eg the parent that barges their tractor size pram and sense of entitlement into a theatre and inflicts their screaming baby on every other patron for the majority of the performance. What people mean is they hate shit parenting, but they tend to say babies instead.