They're the babies of our grown children. I think the thought that the parents are "our babies" is a major contributor to a lot of these issues. When/if ds1 (as an example, as he could easily be a parent within a decade) becomes a dad, I have an obligation to him, my DIL and my grandchild(ren) to remember that I'm not the parent of that child/those children. I had my turn.
Once or twice I even tried to get my mom to see this. I said something like, "You'd think that since you raised me, you'd feel better about my ability to raise my own children."
Ironically, Mom doesn't feel she raised me: she feels I spent so much time with my paternal grandparents (more time than she wanted me to spend, but she gave in to my dad who insisted on letting his parents have me whenever they wanted me), that it was really my Grandmother who raised me, not her.
But really I DID spend more time in my parents' home than I did in my grandparents': it's plain silly the way Mom thinks she's had no influence on me, just because I don't do everything like her.
Any time Mom doesn't agree with one of my parenting practices, she'll say, "Is that what your grandmother did with you?" It's so dumb. Even regarding the extended nursing, she'll ask how long my grandmother nursed my father, like I'd know.
I'm actually not sure if Grandma breast or bottle-fed ... and I'm 43 and Grandma died when I was 21: you know, there are actually things about me that have nothing to do with Grandma, but there's no persuading my mom.:
I'd be truly heartbroken if some day my grown children wouldn't let me have anything to do with my grandchildren. But I still wouldn't see taking my kids to court as a valid option. I think most parents wouldn't want to deprive their children of loving extended family just to be spiteful, and for my own children (or their spouses) to be this spiteful seems like an almost non-existent possibility.
But if it happened, I'd just have to take a deep breath and go on with my life, and pray (and look) for ways to mend the breach and restore the relationship. As I see it, the best way to prevent such a catastrophe is to build a trusting relationship with our kids from day one.