Research why humans take so long before they can digest and eat normal food after being born

Research why humans take so long before they can digest and eat normal food after being born
-Are there mammals that could completely, digest and live off their normal food right away ?
-Are there mammals that digest food right away and drink milk from their mother or a lactating woman ?
-Are there animals that are born like mammals but don't drink milk from their mother or a lactating woman ?

Breasts on woman are a very nice form of sexual dimorphism however.