For many years after I was born we had only 3 channels as well... NBC, CBS, ABC. I don't remember when other networks came into being.... but I'd guess late 60's?

Actually we didn't have a TV until I was about 4... perhaps 3 close to being 4. Until I was in High School I watched a scant few TV programs regularly but mostly I was playing outside.

The first TV show I can recall was called "Cartoon Capers"... and it was the first program to come on in the morning... I think maybe 7am, 7:30 maybe? I don't remember when sign-off was... maybe 1am? I can remember watching the test pattern for quite a while awaiting Cartoon Capers.