Where'd you get the stupid idea Autistic Children don't know they exist? My stepson is autistic and he damn well knows he exists..plus the score of every game a Boston team has played in since he was 5.
Hmmmm... what about newborn babies? They have a lower intelligence level than some adult mammals and can't be considered any more sentient than a dog and certainly not a gorilla.
Self awareness doesn't begin at birth, but long after birth. If whether you can kill a being is based on intelligence, babies are fair game just like monkeys and dogs.
If you base whether you can kill a being based on whether it's a human or not, you have to start at conception, or I guess when it starts dividing into its own distinct cells. And yet the miscarriage rate is very high during early pregnancy, and we don't really mourn those deaths, we don't baptize zygotes, and we don't bury them.
And what is the rationale for birth? It's just a convenient but arbitrary point for defining personhood.