Why a baby is "it"?

Hello!
Can anybody tell me why in English the pronoun "it" is used with reference to small babies?

I don't know that it is. When parents and others don't know the sex of an unborn child, they may refer to "it." Otherwise it is "he" or "she." There was a commotion when someone referred to Conner Peterson (the unborn child who died when his mother was murdered) as "it."

www.lacipeterson.com/

Sometimes people do call a baby "it" in a general or theoretical discussion when they're not talking about a particular known baby. English doesn't have a singular personal pronoun that applies to someone of either sex. So why would we resort to "it" for a baby when we don't for an older child or an adult? I think maybe because boy and girl babies look alike when dressed.