Talking to them and reaching an agreement is the most important thing to do - get a meeting of minds with them. If they wish to use the images for their promotional purposes, and you are happy for them to do so then I would suggest that you retain copyright to the images, but grant them a licence to use them for specific enumerated purposes for a set period, or alternatively in perpetuity if you wish, without charge. It is normal that as the 'artist', unless specifically agreed to the contrary under contract, that you retain copyright and are free to use the images for whatever other purpose you may wish, although you should undertake not to use them in a manner which would conflict with the licence which you grant them (ie you will not compete with them or use the images in a manner which would be contrary to say their charitable objectives). Their payment of the film and developing is payment of associated costs in my view, it is not consideration for your time and skill. A simple one page contract along these lines including perhaps together with some mutual liability indemnification and waiver should suffice They're not responsible for your acts, gear etc and vice versa).
Standard form contracts will be more hassle than they worth. E-mail me if you need help!
Contax IIIa, IIa, Leica M 240, M Mono, MP, X1, DLux 109, Sony A7r, Lumix GH-3.