Hello there Enrique, sounds like a fantastic company you are working for, its brilliant that you are bringing green ideas, especially permaculture and food growing, to all those young minds by installing gardens in schools - keep up the good work!
In
answer to your question, I would say (and this is only my own opinion, please make up your own mind) that, quite apart from the ethical issues, it is really not necessary to include animals (apart from those 'self-willed' creatures that would naturally pass through the system naturally of course, such as earthworms, wild birds, insects, wild
bees, amphibians, etc) in a permaculture system, especially in community or school gardens where they can actually create
alot of unnecessary work. Animals are a huge responsibility and need plenty of attention and care, whether it is buying in extra
feed, making sure they are looked after properly (especially at times when the school or garden is closed), fencing them in properly, cleaning them out, monitoring for disease, fees for vets, obtaining licenses in some cases, protecting them from predators, and so on and so on. As you say, animal droppings and manure can provide nutrients to the system, but it is very easy to maintain and even build fertility without these using plant-based sources such as 'green manures' (in the UK these would include Nitrogen fixing plants such as vetches, clovers, tares, field beans, etc, as well as soil builders like grazing rye, phacelia, fenugreek, mustard, etc), deep rooted plants such as comfrey that bring up Potassium and other nutrients, as well as composting all garden and kitchen wastes and maybe even installing composting toilets to recycle human 'wastes' (an often overlooked urban resource!).
Animal- free permaculture systems can be far easier to maintain, especially in urban situations such as mine, and if something does go wrong with animals in the system the consequences can be far more serious. If I go away for a week or so and leave somebody in charge of watering the tomato plants in my garden in the hot weather and they forget to do it, the worst thing that can happen is I will come home to a few dead tomato plants. If they forgot to look after my
chickens it would be horrendous!
At the end of the day only you can decide whether animals belong in the systems you are setting up, but they are certainly not necessary in my view. Good luck with all your projects, Graham