The only issue I have with this study is whether or not it accounted for mothers, myself included, tend to lean towards their own mother for help with the kiddos rather than their mother in law.
I don't think the paternal grandmothers are included as much in most cases.

Thanks Toad

You are welcome Lisa

Good point, Ljsdesign.

I work with a proud grannie who appears to love her grandchildren equally although one is not genetically related to her. She works hard at not playing favorites. Lucky kids!

Of course there are going to be aspects of your child's personality that you may tend to bond with easier, but favoring has been something I've found disturbing on a lot of levels, no matter if it was a parent, grandparent, or a teacher.
But we may as well rack this up to post-menopause longevity