There are many women out there who have not had, can not have, will not have, opted not to have, are too young or too old to have, etc. children. Yet many of these women exemplify the characteristics of good mothers to children who aren't theirs. Maybe they are aunts or teachers or neighbors or just really kind and sweet people. Whatever the title, they are caring individuals who in a different situation would likely be a good mother.
Likewise, there are many "mothers" whose children would be better off not having them as mothers. While having a child is a difficult undertaking, raising a child is a zillion times harder and more important.
I just want to recognize the wonderful work that non-mothers do. There's not a day for them but they are just as important to the upbringing of children. Thanks, non-mothers! And have a happy non-mother's day!