As far as cameras go most modern ones will record good quality HD footage, even mobile phones, ipods and iPads can do this now. Things to consider really are to check you have a good tripod that fits it and whether you need good quality sound, in which case a camera with a microphone input is importnat.
Honestly you do not need really expensive cameras to make good film. We did end up buying a nicer quality camera at BHS but this was out of the need to film stage productions and assemblies in the hall with good sound and not really for student video creation.
Actually really important if you want to record voice in your movies. Built in microphones on consumer cameras are not up to the task of recording good, clear sound.
A good external microphone can be had for less than $1000HKD and is a great investment. It is important to check though that your camera can accept external mics.
While editing can now be done on an iPad with iMovie it is quite limited in what you can actually do. I would rather teach students using a computer for this job.
If you have access to Macs then I would use iMovie (that comes with all Macs) with the students. It is fast, simple and will give them the needed skills to move on to more advanced software.
If you are using Windows PCs then I would try Cyberlink Powerdirector. It is very much like iMovie and works great. They also provide school wide licenses at a large discount. It is however a paid option. A free option on Windows is Movie Maker, however it is quite difficult to work with and the results can look a little ..... low quality.
At BHS we actually bought 4 Macbooks for video editing 5 years ago. They are still working well now and the software still runs quite quickly.
Lighting is important if you plan on filming indoors. A cheap set of studio halogen lights can be picked up for less than $500 and is really useful if you are filming interviews or shots that nice people to be well lit.
A green screen is useful in some respects and the children love using it. However do think very seriously whether it is actually needed for the movie being made or whether it is being used just for the sake of it.