Crazy Love - S6-E1
Factual error: Carol and Frank leave for a romantic weekend and Dana begins to tutor Rich for a test in English Literature. When Frank and Carol return on Sunday Rich has not only studied for the test but also TAKEN the test and gotten the results back. How is that possible over a weekend?
Answer: According to the SBS website, Brendan's disappearance was never really explained. He just kind of faded out. He was hired as the cute "little" one and as he got older he wasn't as cute. When the Lamberts had the little girl, they got their cuteness factor back and didn't need as many kids around.
Carol and Frank continued to tell people they had seven children throughout the remainder of the show's run, but they never referred to Brendan after season 6.