Hmm… In that case, may I suggest that you start by putting together some simple test program - just a moveable camera and some objects, perhaps - to test the limits of your school computers? That should hopefully give you a better idea of what’s likely to be viable, and might inform your choice of project.
Well, my question came about, I think, because there’s a difference between “no blood” and “nothing even vaguely violent” (and probably because, as I recall it, I don’t think that my own school would have been as strict about such as yours seems to be) - hence my asking about bloodless violence (for example, robots blowing up robots).
However, I take it from what you say that it’s “no violence at all”.
Hmm… You could probably, I think, make a simple jump 'n run game, if I understand your usage of the term correctly. You could probably do it with a single “platform” tile (or more, if you find that you have the time and inclination), a simple avatar (if you think about it you might even get away with not providing animations, and even including a few special effects… ), some collectibles and a goal marker. Instead of violent opposition to player progress, you could, I think, base it around exploration and “keys” - that is, items that allow the player to progress to later areas (these would probably call for a few more models or sprites, but could probably be kept simple, I think).
In terms of such items, there are two types that come to mind: Simple keys, where having the item (or a number of an item, or some other criterion) opens barrier, and items that grant new or enhanced abilities: an item that makes you jump higher, or allows you to swim, or gives you the ability to run, etc.
One way or another, good luck!