Incase you ever have an event like this. Grain of salt though, I'm a youth worker but dont have a degree in child psychology. You ask the child to imagine how the animal feels. Even if the child does not have empathy, the imagine part forces their brain to try to understand. If it persists also seeking professional help never hurts.
This exact thing happened with my cousin. We were staying at a cottage with his family and he had a day where started really enjoying catching frogs and yeeting them against rocks to kill them for some reason. He must have killed like 30 when his mom found out. Then she explained to him that frogs are living animals with mommys and daddys of their own and my cousin suddenly became so traumatized he cried for hours.
I used to love doing these types of things as a child and I was terrified of dismemberment in movies. One day, my dad told me that what I see in movies is what the frogs, fish, and bugs that I'd torment (essentially anything that didn't make terrifying noises) would endure. That was a massive turning point in my life.
Yup, you don't need poison. Just sprinkle some miniaturized union pamphlets on the infestation and the colony will collapse in few weeks. Of course you risk a new infestation of ants with free time, safety regulations, and disposable income.
I think having pets really helps establish that empathy link. Growing up with dogs really helped develop an understanding that creatures are complex with individual personalities just like people. Obviously this only goes so far, but I dont think I would have the same level of empathy and respect for animals having grown up without them.
I think having pets (and being good at it, because not everyone gets this next part) can be really useful for understanding and internalising the fact that animals can have personalities and preferences and all these things we attribute to agency, but also, they're not humans. They don't think like we do, and to value them properly, we need to not anthropomorphise them.
An example of a pet owner who doesn't do this is someone I knew who was getting frustrated with her pet for peeing in her bed. She talked about it as if her cat was maliciously doing it, in retribution for not being allowed out of the house due to illness related stuff. She was so angry and because she felt frustrated at not being able to communicate this to her cat (fortunately, at least having the decency to not physically abuse her pets), gave her cat "the silent treatment" for a day whenever it happened. I tried to explain that if a pet is sick in your bed, it's probably because they felt sick and went somewhere they felt safe, and also that her cat wouldn't understand this "punishment", but she didn't get it. She insisted on seeing an intentionality that wasn't there