I actually regret many things from my childhood. Mostly concerning my father.
(French speaker here, awful English mistakes are coming)
I used to go to his house one week end to two. He was usually trying not to drink too much when I was around, but one day, I guess he could not resist... So he entered in my bedroom, half drunk, and asked me whether I wanted him to hit his girlfriend Joëlle or me. My grand mother had warned me about him becoming violent and all, so I believed him. I thought he was really going to do it.
So I first asked him why he wanted to hit someone. He said that he was very angry and that he just needed to hit on something, but that as my father, he left me the choice. So, after a short reflection, I told him to hit Joëlle rather than me.
Than he began to shout at me, saying that I was an evil little girl, that I was ready so let people suffer in order to stay secure. So I began to fell very guilty about Joëlle. Even now, when I think of it, I feel guilty and afraid, because I don't now how I would react if such a situation arose again. I know I was young and all, but still.
I also regret another story. I was to preschool and there was this little boy I really hated - I don't even remember why we hated each other that much . So one day, I decided to get him punished. I bumped a rock against my own leg several times, until I bleed. Then I showed the injury to my teacher, saying that it was him who hurted me. And he got punished. At the time I felt victorious, but when I think about it now I feel like a bad, decietful girl.