I think most dads and some moms are harder on their own kids but that normally does not equate to less playing time. I also think mom coaches are more fair (on average) than dad coaches when it comes to their own kid.
Not in my case. When it was time to get another girl into the game, I would often pick DD to come out. I very rarely pitched DD (as a starter) on Sunday even though she was arguably equal to our #1 pitcher. She would often come in in relief of the other pitcher. There were many things I did in order to avoid the perception of daddy ball. It got to the point that several parents on the team would ask why my DD was not playing/pitching more!! What I finally realized is that I was treating someone unfairly, but it was my own daughter!! The thread I started a few months back was met with great responses for and against daddy ball and how it is perceived. And I believe I am a better coach (and dad) today because of the advice of some of the people at DFP.