I'm a living example of someone that had anger issues as a kid and yes I was mean to animals (I also would drown some living things, decapitate frogs, etc). However, I'm totally different now and have been for the longest. Yes, now as an adult I do look back at my past actions back then.
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It has to do with empathy, or lack of.
Children often lack empathic ability and that's why they can be cruel.
With age people usually develop stronger empathic ability and they are no longer cruel because they feel with the animal and other people.
Some people are psychopaths and some never really develop empathy, hence can be cruel in adult age.
So the bottom line. It doesn't matter if you've done cruel things as a child or not. What matters is if you develop empathy or not at a later age. That's my 2 cents.0