I watched a documentary ages ago where it did tell you why we found babies cute. It's down to genetics, and the way a baby looks....small mouth, huge eyes, etc etc is all designed to make us go "awwwwww" and want to protect them, so we do.
From what I remember about the little bits of psychology and ethnology I've studied, it's to do with the big eyes and (in the case of humans) the comparatively large head of a baby. Eyes don't grow, as far as I know. We're all born with the same sized eyes we have throughout our lives, but in a child or a young animal, they appear very much bigger. I think this, along with their scent (which we often register subconsciously) enhances their vulnerability and need for protection.
Wasn't there something similiar about attractiveness? If I remember rightly, the same features of a baby are what adults tend to find attractive in each other - clear skin, large eyes and large lips.
Well sorry to have to say it, but personally I find human babies absolutely disgusting. They are ugly wrinkled smelly noisy little bundles of puke and sh*t.
Now give me a puppy or kitten, or even a baby reptile, and thats a different matter. There's no smell on earth like a baby puppy, its just wonderful, all sort of wheaty.
I never cease to be amazed at the birth of an animal, and how they find their way to their mother's milk.