Seatbelts and doors. That's it really. And "do you need the loo before we go?" as I said before.
Anything else: as it comes. If they talk when I'm trying to listen to the radio, I say "Shh a minute!". People get the idea pretty quickly. Long drawn out briefings on things they can't do anything about just worry people.
As for keeping hands and feet off controls: passengers are normally more worried about that than I am. If a passenger is so stupid that I need to warn them "don't touch the controls" then I don't want them in the plane.
Kids: obviously more instruction (and an additional responsible adult in the plane).