Thank you all some really good advice here, i always thought "why am i telling them about this" when breifing engine failures. In answer to MIKECR's question This kind of PAX briefing is part of the exam check flight and i was taught to breif passengers this way. Infact after breifing one instructor about what i will do if we had an EFATO he let me climb to 300 ft and promptly closed the throttle and sat back with arms folded :-) when i asked what he thought he was doing he said "you breifed me on it, and we've had one, where are you going ? <to put it down>"
I think its sensible to follow your advice and brief them on the need to know stuff, seat belts doors, vents, odd noises, no talking at times, don't walk forward of the wing :-) etc.. I always ask on take of and landing phases they have arms by their sides and feet on the flooor and show the the rudder peddals to explain why, then i tell them 'we are in the take off/landing phase' so they know.
I also have a little trick that a comercial areobatic pilot taught me, the "Thumbs up/Down" approach. He said sometimes you won't get a verbal response, so Thumbs Up = i'm ok lets keep going, Thumbs down = Lets go home. I did this with my young nephew on board (who usually talks constantly) and never got a verbal reply just a thumbs up and a smile.
Thanks All very useful,