“Mister Monkey” --- a screwball children’s musical about a playfully larcenous pet chimpanzee --- is the kind of family favorite that survives far past its prime. Margot, who plays the chimp’s lawyer, knows the production is dreadful and bemoans the failure of her acting career. She’s settled into the drudgery of playing a humiliating part --- until the day she receives a mysterious letter from an anonymous admirer…and later, in the middle of a performance, has a shocking encounter with Adam, the 12-year-old who plays the title role.