Other mistake: Season 5 sees the family celebrating and reminiscing when the children came to live with Uncle Bill. Buffy and Jody were 6 when they came to live with Uncle Bill. This would make the twins now 11. In a later season 5 episode, Jody is trying to get a female classmate to like him in order to secure a stamp he wants for his collection, the Spanish triangle. His antics catch the concerned eye of his Uncle Bill who asks a few times during the episode, "is it normal for a 9 year old boy to be interested in girls?"
Family Affair (1966)
1 other mistake in show generally
Starring: Brian Keith, Anissa Jones, Johnny Whitaker, Kathy Garver
Other mistake: Jane Webb is listed in the closing credits as "Store Lady". She actually played the "Story Lady". (00:25:00)
Trivia: In the season 5 episode "It Can't Be Five Years?" the woman playing Uncle Bill's secretary is Sebastian Cabot's daughter Annette.