The Dragon of Pendragon Castle (1950)

Sir William Magnus lives in an old drafty castle with his daughter and his two grandchildren, Peter and Judy. Few visitors call and when there are guests they do not stay long, freezing cold as the place is. One day, in the company of their playmate Bobby, the castle's only servant's nephew, Peter and Judy discover a sick baby - dragon. Far from being terrified, the three kids immediately understand that the little monster will be their savior.