I'd agree with those who've said babies, as 0-2 Int creatures, have animal intelligence and are thus incapable of moral choice -- they're neutral.
By the time they can haltingly speak a language (at about Int 3), they're still usually neutral.
Late toddlerhood/early childhood (ages 5-8 ish) are about when the thougts take on a moral pattern, and most by then would have game-term Ints of 5-8 themselves.
And still, most humans are neutral. They look out for themselves and those they love first.
Though, the birth of some demon-spawn or something can easily be evil from birth. Fiends and outer planar beings are evil from inception, and half-fiends and tieflings, though perhaps born neutral, usually are swayed to evil because it's natural for them.
Any humanoid is probably neutral at birth; the alignment is largely a culturally determined factor, though it may have fiendish origins (the legend of Gruumsh corrupting elves to make orcs lends itself to a belief that he was a fiend who attracted some elvish worshippers and eventually grew to dominance over them, perhaps sending emmisaries or using his own power to warp their minds and bodies, inclining them to evil as they mingled with fiendish blood...theoretically, orcs could just be elf-tieflings who have fallen very far from the tree...).
It might not be a bad idea for a midwife (probably an adept, given how close these figures often are to the forces of life and death, and how much they are often associated with mysticism) to take detect evil in a land that's suffered from many fiendish trepedations and such. Fiends diguise themselves as many things. Make no mistake, the cute mewling larvae that is born is merely a fiend in a different guise, fully aware of the evil it causes and delighting in it.
In a land such as this, the midwives have to be very trusted -- it's a trust that's fully subjectable to being perverted and misued for personal ends. Like, say, the midwife is the old favorite wife of the king and, to spite his rejection of her, she finds that all his children are fiendish and has them dealt with. Perhaps she even starts spreading the rumor that the king himself is a fiend that must be destroyed, and is just using a cunning guise. Maybe she pays some guy at the local tavern to spread the rumor in a sad song, and, maybe, recruit some happy little adventurers to do her dirty work for her and kill the king. And maybe, if they actually succeed in killing him, the midwife can actually contact some form of fiend for her own glee, perhaps eventually taking levels as an evil cleric and challenging the party at many future junctions...
...though that's just a random thought.
