Not to know what happened before one was born is always to be a child.
I found this Cicero quote on Lapham’s Quarterly’s about page. A little research dug out the supposedly original version found in Orator Ad M. Brutum (46 BC). It goes like this:
To be ignorant of what occurred before you were born is to remain always a child. For what is the worth of human life, unless it is woven into the life of our ancestors by the records of history?