Christian name?

here is a quote from the questions and answers section aout the name johnny belinda

Johnny Belinda is the name of Belinda's son, who was named in Gaelic patronymic tradition. In Scotland, as well as parts of Scottish Canada (e.g., Nova Scotia, Cape Breton, Prince Edward Island), people are often referred to by their first name followed by the first name of their father (or husband, in the case of married women). So a man could be officially named John MacDonald, whose father is Alec MacDonald, but might be called John Alec. If John marries Catherine, she will be called Catherine John or even Catherine Alec. Usually it's the father's name that is taken, but occasionally it's the mother's name, as is the case in this movie.

her sons first name is johnny and sometimes they take the mothers name back then, hence his last name from his mom Belinda