That's a great idea, Rachel. I would just comment that it might be worth taking a good look at any old stuff that comes in. Old guitars can often need more than just re-stringing to be playable. One with a wrongly set or bowed neck (for example) will be unplayable - with the end result that your budding players may be put off for life!

Dick's suggestion of ukes as an alternative is a good one.

If I see anything halfway playable in any of the charity shops that line local streets, I'll bag one for you if I can.