Well, in the show Gabriel and Edith's children have been shipped off to boarding school. They're never shown, and hardly ever mentioned. In the 30th Anniversary of the DS Almanac, it says that Gabriel and Edith have three children, only one of whom married (all of whom are labeled as "Unknown" including the married one's spouse). The married child has Edward, Judith, Carl, and Quentin as children. So, it's possible, I would assume, that the "Thaddeus Collins" that David mentions, COULD be one of Gabriel's children.
Their ages would've been a bit wonky, but it would've worked because back then they had children at a young age.