Children have no concept of violence or empathy or right or wrong. Children often are extremely violent to other kids and sometimes even adults. They kick they scream they punch and they destroy objects. It's on the parents to teach them these concepts and its fun to have settings in which that behavior is allowed.

> As a child I did not see it as violent

That's the problem. Hitting a tied up animal until it breaks is clearly a violent affair, similar how hanging puppets in nooses or putting a doll in a guillotine.

I'm sure that there are kids growing up in places where bullfights are common thinking that torturing and killing a bull in a party-like atmosphere is fine.