One afternoon, when I was about 8 or 9 I walked into my parents bedroom to put something away. Unbeknownst to me, my Dad was in there changing. He had no underwear on and I remember being stunned and immediately covered my face and turned and ran out of there. He quickly covered up and went 'Whoops, whoops". I had never seen a man's private parts before that, only my little brother's. Seeing him in that state kind of scarred me for a while and that brief memory still makes me cringe all these years later.

As such, I can see no reason why it would EVER be a good reason for a grown man to shower with his daughter AT ALL. I would never let my husband shower with either kid.