A well known actor portrays a teacher who conducts a class for kids learning to be pickpockets. A girl asks to join the class. I thought the girl was maybe Ginger Rogers, but I can't confirm that. The movie may be on You Tube. Who is the teacher? Who is the girl? And best yet, what is the movie?

Sounds like one of the various "Oliver Twist" adaptations. There are so many I cannot list them all, but that's a starting point.

Heartbeat (1946) (https://www.youtube.com/watch?v=0bQxpSnAfKY)
Starring Basil Rathbone and Ginger Rogers