If you want a light comedy, then I think they should have a couple or 3 kids.
Since we are operating on the premise of a movie made in 1961, we could jump-start Mel Gibson's acting career and have him be one of the kids - he was 5 years old in 1961. Hayley Mills could be the teenaged daughter of the family. Kirstie Alley could be the feisty middle child (also jump-starting her career as well).
Mrs. C