And don't say Bert Lahr's kid.

First clue: It was a first on the silver screen.

Second clue: It's from a movie in the 1940s.

Third clue: The baby, in the movie, is looking up at his parents, who are about to die.

Fourth clue: The real name of the baby isn't famous. It isn't even known. It's who the baby is playing.

UPDATE: Longtime reader Reed got it below. It's the first, live-action, screen incarnation of Kal-El, or Superman, in the 1948 serial “Superman,” starring Kirk Alyn. If anyone knows who played the baby, let me know. IMDb.com doesn't have it.

I will now update the tags, etc.