Given how old it is, the Family Affair episode is very nicely done, particularly the very end, which credits children's feelings without verbal exposition, and shows that the parents have misjudged what the child is capable of feeling and understanding. It is also super-sad.
I'm sorry, but was it not Blossom that put the term "very special" on the map? I wish I could think of one in particular, but I know there were several.
Hanks' performance on Family Ties is the one that really sticks with me (potentially, I blocked most of the others or they didn't have the impact on me at whatever age it was I watched them). The moment? Going after the vanilla extract.
I'm still not convince the mime killer episode of Little House isn't an elaborate joke by the internet.
The episode of Diff' rent Strokes where Kimberly and Arnold get kidnapped after accepting a ride from a stranger always stuck with me more that the classic Gordon Jump episode. Arnold gets away and leads everyone back to the scene, where they find Kimberly in the basement storage locker just in the nick of time.