Babies that have only ever eaten milk are made of milk, so they’re basically sentient cheese.

Oh it goes deeper than this -

Baby's are made of materials floating around in their gestational parent's blood. And guess what breastmilk is made of..... It's made of blood. Your body literally takes your blood and turns it into milk.

So until they start eating food, a breastfed baby is made entirely of their mother's blood plus a single sperm.