I'm not saying that I wish we had kids for this purpose--as that sounds like a really bad reason to have children--but it makes me sad that my DH might be alone as he ages.
Still having children is no guarantee they will visit an elderly parent or pay attention much/at all. This most definitely would be heartbreaking to any parent.

What is important to me, since I chose not to have children (he has 2 from a previous marriage), is comfort/knowledge that I have several blood/family relatives younger than my generation which we know one another over the years. This is important to my own sense that I exist connected (no matter how tenuous) directly to a network of family members. I'm sure there are some who are/end up all alone as an only, child-free individual..no nieces, nephews, aunts, uncles and all parents/grandparents no longer living. I do know someone who became like this in their early 50's....which is early.

But she is a socialable person who seems to attract alot of goodwilled friends, etc. A great trait.