Although the show ran for eight years, it only actually covers a four-year period, despite some time-specific references (mostly notably the Millennium-centred final episode). This was partly for storyline reasons, as the first episode of a new series would often pick up immediately from the previous one, and partly to prolong the potential life of the show by not having the Porter children age too quickly.
When Georgina Cates left the role of Jenny Porter, twin sisters Clare Buckfield and Julie Buckfield - who were already playing twins in Grange Hill (1978) at the time - both auditioned to replace her, with Clare winning.
The title comes from the stereotypical average size of a typical nuclear family in the UK at the time of the writing of the first series.
The show was initially pitched to Central as a sitcom called Hell and High Water. Ben was absent from the pitch, with Bill being a widow and she working for her brother-in-law (intended to be played by Freddie Jones) selling souvenirs at a seaside town. Rona however was already fully formed from the outset.