Here are some facts we have collected over the years about his children
Q. Do Columbo and his wife have any children? More than one?
A. Good question -- depends on the episode.
In "RIP, Mrs Columbo" he claims he and his wife never had any children. But then he was talking to a homicidal maniac who was trying to kill his wife, so Columbo may have lied to protect his family.
In "The Most Crucial Game" (1972) he says the wife complains that the ice cream man comes before dinnertime and spoils "the child's" appetite.
In "Any Old Port In A Storm" (1973) he says he went on a picnic with the wife
and "my kid". Might have had another child too young for the picnic, because in the same episode he needs a babysitter and b**s 2 quarts of milk, and says "You know how it is when you have kids."
And he says it's too hard for him to write a book at home with "the family and all,"
which sounds like multiple kids running around ("Publish Or Perish," 1974)
In "Mind Over Mayhem" (1974) he says the wife and "kids" are visiting his
mother-in-law.
The likely explanation is that Columbo's family grew during the long run of the series. He was married in 1966 , only one year before "Prescription: Murder"
(25th anniversary in 1991 - "Death Hits The Jackpot" ).