I obsess over the past too but I find that it helps when I'm extremely busy to not think about it. Just know that 8-12 years old is sooo young! You can not possibly compare your judgement and morals of today to yourself at 8 years old. If you did things, it was out of exploration and ignorance. It was not your fault, you just didn't know any better. When I get regretful thoughts, I push them away and say good things about myself and that I wouldn't do those things today which is what matters. I also imagine the bad thoughts into a little bubble and mentally pop it. If the thought creeps up again I literally don't think about it if you know what I mean. I push it away and ignore it as if someone is talking to me but I'm not taking notice.