First Stop - S4-E14
Continuity mistake: In this episode, Fred and Ethel claim that the bed they are sleeping in is just like the one they have been sleeping on for years. It is double bed with a big sag in the middle. However in an earlier episode "Vacation from Marriage" they show Lucy and Ethel in the the Mertz's bedroom and they have twin beds.
First Stop - S4-E14
Continuity mistake: When Ricky stops the car and backs up trying to locate Aunt Sally's, Lucy gets out of the car wearing a coat and a pantsuit underneath, but in the exterior shot she's wearing a skirt set when she walks over to the shed to read the sign. (00:03:50)
Answer: According to Snopes.com, there is no definitive answer, but the mid-1960s is the most verifiable date with "The Munsters" being cited as the first, although others claim "The Brady Bunch" showed the first couple seen in a double bed. An early TV show from the late 1940s titled, "Mary Kay and Johnny" is also thought to have shown the married couple's bedroom as having a double bed, although probably not with them in it. However, this was when TV was aired live, and there are no surviving episodes, only anecdotal accounts.
raywest ★
Something that is funny is that in the movie "A Christmas Story," they show the parents having two twin beds in their bedroom. In a real situation, they should have shown them having a double bed. Lucy and Ricky had twin beds pushed together in an early episode, which would have been pushing television boundaries in that time.