[RiderOfGiraffes]

Teaching kids about computers is great, but given your limited time, and the limited availability of kit, my personal feeling is that you'd be best spending most of your time teaching them basic science. Having a good grasp of doing experiments, measuring things, and general problem solving, is of great value in everything they may end up doing. Teaching them "about computers" pretty much only teaches them about computers.

In the end, though, it is your judgement. You have to teach them

a) what you're comfortable with

b) what they will respond to

c) what seems to provide value, short and long term.

I think basic science is better than "about computers", but you'll be the man on the spot, and it will be your call. I think you're doing a fantastic thing.