From Ingmar Bergman's Fanny And Alexander: there is a rehearsal in a darkened theatre of a scene from Hamlet. Alexander's father, playing the Ghost on some creaky battlements, collapses from a heart attack. His small son, Alexander, is watching from the stalls. As the chaos builds behind him, the camera slowly 'dollies' in on the small boy's face. There are wonderful echoes of life imitating art.
There is a wonderful scene in Les Enfants Du Paradis by Marcel Carné and Jacques Prévert when the actress Arletty, playing the character Garance is arrested. She managed to combine great sex appeal with an insolent humour. 'Ne me touche pas! Fragile! Objet d'art!'
My third would be almost anything from Charles Laughton's Night Of The Hunter with Robert Mitchum, but particularly the scenes when the children are fleeing down-river with the nightmare closing in on them