Estrangement in any family can be very painful. If the reasons are understood, then maybe dialogue can help construct a form of bridge to help families to reunite and even heal. Forgiveness can go a long way to create peace in our lives. Abandonment can often lead to regret. Even if a parent is guilty of poor parenting skills, sometimes it's best to air these feelings and let it go. I was raised during the days when spanking was socially acceptable, not beating or abusing but as a way of controlling children when they misbehave. It left no emotional scars on myself, my siblings or any other neighborhood kids. It did not teach us to hit or be violent with others or our own children. Schools also used it as a tool for grade school children and believe me, when I was in school children behaved pretty well.
It isn't easy to figure these things out because if it's only one child, say, out of a brood of five, you could scratch your head and wonder why. I have a neighbor in her eighties, widowed, who had four children--three of which visit her all the time. When her husband passed, I noticed the name of another daughter that I had never met. Innocently, I said to her, "oh I didn't know you had two girls, does she live far away?" To which she said something like, no, she lives a couple miles away, we are estranged but I have no idea why. Ouch. I didn't know what else to say but I wasn't trying to be nosy, and I am very sorry to hear that. Last week, I visited this lady and she told me how bad her year had been. She lost a dear daughter-in-law, her sister and her estranged daughter! How painful that must be.
I look at things differently, maybe, than some people. We have the ability as adults, to maintain boundaries. If the problem is with a parent that is intrusive or demanding, limit your exposure. You can get your point across without being indifferent. Keep phone calls brief, send a card. Encourage children to have a relationship if possible, allow them to get to know their grandparents despite the relationship of the parents.(unless, of course the kids protest) Grit your teeth and visit once in a while, you can keep visits brief too. Just try not to eliminate them from your life completely unless circumstances are so terribly bad you cannot find it in your heart to do this.
My older brother and sister had an estrangement with my Mother, for a couple reasons I fully understood. A couple years before she passed, amends were made and I for one, so glad. They had her to their homes for extended visits and that is all she talked about for those two years. I don't know if they ever trully forgave her but what they did was get passed it. We cannot change our pasts but we can either chose to forgive or try to let it stay in the past and move on. It requires one to first extend that olive branch. It may be "freeing". Life is short.