Inoffensively sentimental, the Scotland-set Dear Frankie follows a single mother (Emily Mortimer) who is trying to keep her 9-year-old son from the harsh truth about his missing father by claiming he works on a ship that is always off on far-flung journeys. When the boy starts pushing for answers, she hires a stranger (Gerard Butler) to stand in as his dad. It is a sad situation, but director Shona Auerbach gives the story an aching sense of humor. The mother’s increasingly convoluted scheme is futile, yet she keeps at it in an equally futile attempt to prevent her son from growing up.