In reply to Kean:
Well, session one was this morning: 3 to 6 yr olds. It went well but very surreal experience. I said to the organiser "I'm not QUITE sure what I'm doing." She replied "Welcome to our world!"
40 of them with approx 4 helpers. First weirdness for me was being peered at by all these wide-eyed tots and being billed as "the expert".
My grand entrance was me dressed in full ice climbing kit, trailing a rope attached to another rucksack out of sight in the adjoining room. I asked a couple of tots to lend a hand hauling and suddenly had 40 gnomes scrambling for the rope to get in on the action. Great fun. Then I changed into rock climbing gear. Then I started introducing a mix of specific and general terms in easy English, ranging from boots to trousers to rope...big surprise for me when I pulled out a compass...they were totally, mind-bogglingly fascinated by it (compared to "boots" and "socks", about which the consensus was "smelly"). I had to go round the entire group showing it to them. Then we played a memory game, with them chorusing a set of vocabulary. Then I let them loose on all the gear. Then I dressed some of them up. Pretty endearing seeing a 5-yr-old tot of a girl dressed in oversized harness, boots, jacket, helmet, brandishing two ice axes...and clutching a teddy bear!! Finally team photo with them all clutching a climbing rope.
I also had the short video and some stock photos kids climbing.
So all in all it went OK as a first attempt. Needed one or two more structured activities and a tad more interactive English but thanks to the many great pieces of advice offered I think I managed to avoid a fair few pitfalls and they enjoyed themselves.
Tomorrow, 6 to 12 yr olds & I should be able to set up a few more activities.
Sincere thanks again for all the great advice.