Bibbity. What age do you think they will be old enough?
To me, and I cant say I have given it a lot of thought up to now, I think with most things, children learn things bit by bit, and daily about all sorts of things. And I would include learning about relationships with both children and adults in that.
Though of course, even if they did not get grandparent contact, they still learn about adults through nursery, school etc.
They can indeed be altered by actions and words of others. Most definitely. But they then also learn from parents how to deal with things that may be hard to deal with.
To a certain extent, the practice they get, while they are being very well looked after by those parents, is a safe way for them to learn about adult relationships, if you see what I mean?
In other words, they learn, just like they learn about all sorts of other things.