I think people can be honest about their regrets, to people other than their kids. I'm sorry that your parents regretted having you, and they couldn't find the ability to accept and be happy in a life with you in it, instead of dwelling on an imaginary version of their lives that they think would have been better if they hadn't had kids.

Like yes, people shouldn't have to have kids they don't want, but once you DO, and if you choose to stay the parent and not put the kids up for adoption, I think that it's incumbent upon a responsible parent to learn how to be happy in their present situation and to heal whatever is making them dissatisfied with their life as a parent. So that they don't constantly have this narrative of "my life would be better if I didn't have kids, I wish I didn't have them", because that's going to express itself in their actions and how they treat their child.

Acceptance and commitment therapy could be helpful for parents in this kind of situation. It's an essential life skill to be able to go "this isn't the future I would have chosen for myself, but now that it is my life and I can't change that without majorly harming people I'm responsible for, I need to find a way to come to terms with this and find peace and happiness".

This isn't just for parents, this is for anyone who's experienced hardship or trauma, lost loved ones, lost opportunities etc.

Then such a parent could tell their child one day "I didn't choose to have you, and I would likely have made a different choice at the time if I had known, but where I am NOW, is that I love you and value you, and I'm glad you're here with me on this journey".