The first strip. Say what you will about the strip now, it was Actually Pretty Funny. It showed Thelma looking tired talking to somebody at the door who asks, "Any Children?". And the floor is covered in toys.
A 1970s strip shows Thel running through the toilet section of a hardware store. "No, Jeffy! It's not connected!"
From 1982, Billy has swimming flippers on and ponders to Dolly, "I can see why frogs don't dance much."