Yes, I know it's just a manga, but there's a possibility that the mangaka thought that readers would assume that the MC heard about it from his grandchildren (or maybe his great-grandchildren) at some time in his life.
And he's not three years old. He's seven, I believe. There was a page that said "six years later" after he was shown as a one-year-old.
no, it said two years later
I don't know why I read six, lol.
Well for all we know he could’ve died in this era, and maybe the god erased all his personal memories but not memories that had no relation to his past life
nice story
but considering how old he was, how did he know the classic reincarnation tropes of today, and why does he come to the dangerous conclusion to go to the forest as a three year old?