A Pile of Goo
Maybe it's how they bring out the softer side, or maybe it's just how they fit into strong, masculine arms, but there is something about a man holding a baby that just drives women wild.
Take this subject, for example:

See the way he is looking at her? Does it make you melt with happiness into a pile of goo? No? How about this:

I am sorry - but that might be the most precious thing ever. EVER.

…Or maybe it's this. I'll let you know when I decide.