Dick van Dyke and Hope Lange, likeable stalwarts of 1960s sitcoms made a second series together with pretty good results. No particularly memorable plots but you really believed them as a modern married couple with a young teenage daughter.
The writers wanted to make a more modern series; this was after all the era of ALL IN THE FAMILY. That led to the one scene that people remember from the show and a scene likely to appear on TV comedy retrospectives-- It's night time, the daughter is asleep and the parents have gone off to make love in their bedroom. The camera shows the hallway linking the two bedrooms. Out of the door on the right, the daughter comes out, calling to her parents in a sleepy voice. She crosses to her parents' room, opens the door, and enters. Wait two beats..... On the third beat she backs up back into the hallway and silently crosses back to her room. Wait two beats.... The parents, hurriedly tying bathrobes shut, head to the daughter's room!
A nice scene follows where the parents try to explain what the daughter saw. The daughter listens intently, nods her acceptance, and then giggles the punchline, "You two sure looked funny!"