carvaka -
For whatever it is worth, I don't personally believe in trying to 'delete' memories. The past is the past, what happened happened, and selective memory potentially can be result in a very confused understanding of ourselves.
Instead I would try to see those old memories in a new light. In this case you were both young kids, limited life experience, your intellect and awareness of self/others was still developing. You are now both older, you're not the kids you once were.
For example I took some other kids toy truck at age 7, but I know now as an adult that's not how to treat others and I don't steal. I'm not going to beat myself up over something I did as a child forever, and I'm 99.9% sure that other kid has long since gotten over it too

That's not to make light of your question, as there is clearly an aspect affecting you now, but really if you two had a fight at age 7/8 or any other regretful interactions, you'd have written it off as the past.