Stop thinking about your parents for a moment.
Ask if you did the best you could, with what you knew at the time? I constantly beat myself up for not doing better but the truth was I was just trying to survive and I truly couldn't do any better because I didn't have the necessary education or resources.
An integral part of healing from your trauma is also realizing that your parents were most likely victims of their parents too. Inter-generational trauma is real. Bojack Horseman actually addressed inter-generational trauma and how it wrecks the lives of children very well.
I truly believe that you have to recover from being a victim or risk turning into the bully later in life. I used to have some friends from school who were from similarly messed up families and we all bonded because of our pain. I ended up having to cut contact with them when I saw that their pain also causing them to bully other people. On your healing journey you'll realize how important it is to have positive role models in life and those of us who have CPTSD because we come from extremely turbulent families did not have a single healthy role model in our lives, this is why we're flailing so hard as adults.
If "your mum did the best she could with what she knew at the time" doesn't work for you then maybe rephrasing it might help? "My mum was not equipped with the right education, emotional maturity and resources to do any better and she probably still isn't. She could not be the parent that I needed when I was a child."