No.41837
Because puppies and the majority of other animals even if they grow up, don't pose a threat to the average human, so you feel that seeing them suffer is "unfair", leading to an universal disgust towards that. Children are a bit more tricky, the majority would still hate to see something like that, but others rationalize it with the fact that one day they'll grow up too and they'll stop being "harmless".
No.102277
i think it's because people usually have more negative experiences with children than with animals