i brought this up a few years ago and some die hard fans had a fit about it. you can see by the way she looks at him that she was smitten. she was just a young girl. nothing wrong with that.
There's also an episode where they are at a barn dance and they start dancing in a very close, very non-brother-and-sister way.
And there's a scene where John-Boy is off to school or out or something and he plants a goodbye kiss on Mary-Ellen's *lips*, like how you would say goodbye to your wife. That's Richard Thomas initiating that; she is just sitting there passively.
I heard they were getting it on in real life at the time.
Wow. Its a joke. You know how they say all mountain people down south sleep with their sisters. I love the first 6 seasons of the waltons but have a little fun why don't you.