Ever hear of a French novel called Les Miserables. I think they did a musical about it.
I hope I’m not going astray of what the OP wants, but it’s hard for me to imagine a story involving a foundling where the foundling isn’t a catalyst for great change for at least the finder.
I searched the thread for Charlie Chaplin, and got no hits, so I’m guessing nobody’s mentioned the classic movie The Kid.
Does a mother dying in childbirth in an otherwise male community a foundling make? No? Well, still, I’m mentioning The Luck of Roaring Camp.
Well, as a foundling, anyway.
Said foundling was separated at birth
Highlander?
A Bedtime Story, starring Maurice Chevalier.
“The Graveyard Book” by Neil Gaiman.
While he doesn’t seem to impact his adopted family’s life too much, Carrot has an effect on Ankh-Morpork in the Discworld series.