I'll have to find some comments to add to this thread, as I feel this is "my subject", (or one I keep banging on about anyway), but I'd first like to endorse most of the above comments.
It will be too easy for me to repeat things I've said before, or in fact very hard for me to avoid doing so completely, but if I state a few facts, perhaps that will be helpful to someone, ("as an excluded parent of twenty four years and counting"!).
My daughter aged twelve stated: "that even if a judge ordered her mother to allow me contact with her, she would not come".
My daughter has stated on many occasions: "He ruined my life until the age of twelve, dont let him ruin any more of my life".
My daughter stated: "He never took me anywhere interesting on contact visits", and her mother and "new daddy" stated: "It was cruel to take my daughter to church when she did not wish to go".
My daughter stated: "Every letter he sends me makes me more pleased I dont have to see him anymore".
In spite of all the above, my daughter, possibly persuaded by her husband, allowed me to be present when she brought her six months old son to visit the farm where my father lived, a year before he died, so four years ago. My daughter chose to stand beside me at my father's funeral, in a large church where there was plenty of room to stand elsewhere, and although I'd tried to let her know the funeral details I'd no idea she was going to attend. My daughter remains as the sole beneficiary of my will, although she'll never need any money I might leave, and in my opinion she had a wonderful childhood, added to by my ten or so years of contact with her after my wife broke up the marriage, (a time when she repeated often "Keep coming daddy", though she did not have to say this).
Therefore, when you ask "what do we owe our adult children? or grandchildren?", I'm left thinking why it is so abhorrent to people in western countries to suggest our children owe loving parents and grandparents a great deal?
Why is the focus always so much the other way, and is this a good thing, (I'd suggest not, and a change in family law to reflect at least a more balanced view, is well overdue

?