The Shaggy Dog 1959 with Fred MacMurray, Jean Hagen, Tommy Kirk

The son of dog-hating former mailman Wilson Daniels (Fred MacMurray), young Wilby (Tommy Kirk) accidentally becomes a canine himself when he stumbles upon an ancient curse. Inadvertently invoking a magical spell engraved on a centuries-old ring, Wilby begins turning into a sheepdog at unpredictable times, only to later return to human form. As if this wasn’t enough for Wilby, he overhears a plot to steal secret government information while in dog form, leading to unexpected adventure.