Why do we like playing dress up?

Why do parents and grandparents get their kicks from dressing up their kids? I always said that I would never be that mother who put their kids in ridiculous outfits. I thought I would always dress Kate in trendy outfits, not those frilly girly clothes.
We were taking her picture last night in a pajama outfit my mom sent her and it hit me. She is only six months old and I have already done (several times) what I thought I would never do. The bunny pajamas came with a little bunny hat and everything. We thought it was so funny, so we took some pictures.
It reminded me of that clip from A Christmas Story when Ralphie's mom made him put on that bunny outfit his aunt gave him. I have it posted below. It makes me laugh when they scan to his little brother laughing hysterically at him.
Oh, Kate, I hope we will not be that bad. You can see in these little compilations of her photos. She starts out happy. By the end she is looking at us and I can hear her saying... Seriously people, I have had enough.