It was probably someone VERY desperate for their kid. Cause there wasn't exactly a place to buy baby formula, and the state of prehistoric maternity care was… poor, to say the least. So they thought "hey, if it is good enough for the baby cow, it must be good enough for baby babies."

Now the person that first ate cheese- that is a sick mother fucker. He saw that a thing of milk had turned yellow and solid and decided "fuck it, Imma gonna eat it anyway".

To quote portal 2 'The first person to prove that cow's milk is drinkable was very, very thirsty..'