The Philadelphia Story (1940) Virginia Weidler (died of heart attack aged 41)
Meet Me In St Louis (1944) Margaret O’Brien (she was only 7!)
Leave Her To Heaven (1945) Darryl Hickman (good bio on IMDb!)
Mildred Pierce (1945) Ann Blyth (well, she may be teenage, but she’s only 16, and she’s so great she’s in) and Jo Ann Marlowe
Pursued (1947) Ernest Severn (came from South Africa, never worked again)
Red River (1948) Mickey Kuhn
Shane (1953) Brandon De Wilde (knew him, though only for his haircut! Died at 30)
Hondo (1953) Lee Aaker
The Night Of The Hunter (1955) Billy Chapin (Violent Saturday) and Sally Ann Bruce (never acted again)
The Searchers (1956) Natalie and Lana Wood (sisters playing Debbie at different ages!)
Stroke of luck 