Let me start by saying that I am speaking from a position of experience in this field. I have written technical training for summer camps, taught for three years a summer camp teaching game design/programming using Game Maker, and currently mentor high school students in using Game Maker to design and build computer games.

I am not sure where other people have been getting two days from since it appears you mentioned that the camp will last for two weeks. Two weeks is a reasonable amount of time for a summer camp program.

There are a number of factors to consider when picking technology for a summer camp project. The most obvious question is what sort of computer resources are available? School computer labs are usually fairly substandard. Also IT typically has computer lab computers locked down pretty tightly and fighting the administrations to get the correct software installed can prove difficult. If you are going to use a 3D engine and especially a modern 3D engine then you will need to ensure the computers have modern video cards (on board graphics for something like Unreal Engine 4 probably won't cut it).

I originally tried C#/XNA with my middle school students but that proved very difficult. The hardest part was the typing speeds of the students. I was not only trying to teach how to program and how to make a game, but in some cases I was having to teach basic computer skills and typing.

Game Maker is a nice choice because you can start the students off with the visual scripting and then move on to the more advanced GML scripting. It allows the students to be productive fast and that keeps them from becoming bored or frustrated.

I have avoided trying to have students make a 3D game because of the complexities introduced with regards to the math and the graphics. 2D art assets are far easier to draw and the programming is simpler. I think it might be hard to explain things like quaternions, rotational matrices, and shaders to that age group.

I know you said you must make a 3D game but this is just my thoughts on the matter. My main advice is just to make sure you know what the system specs on the machines you will be using are and to test any candidate software on the computer to ensure that it will work.

Thank you for your answers. I will answer some questions and concerns that were asked.

So the reason I need to make a 3D game is for marketing purposes. This summer camp is part of a bigger one that has many other science camps (Biology, Chemistry and many others), but it also has another, smaller, 1 week Computer Summer Camp, aimed at 9-17 years old. That summer camp includes Game Maker (a very brief introduction, with most of the work already done), so it has to be drasticaly different from that one.

This summer camp is to introduce students to game making, working as a team, 3D modeling and texturing. An example of a project we did last year (using the Blender Game Engine) is a simple 3D platformer where the player would run to the exit, avoiding some obstacles. It wasn't a great game by any means, but it taught them some basics.

Blender is really menacing, with options to do some extremely complex stuff and the game engine is complex, but it's a bit too confusing for first time users. I am really exploring other options for this year. If I don't really find any, I'll stick with Blender.

The computers are university computers, so they are not that weak either. I would have problems convincing IT to install UE4 or any really big engine. What I would really need is a 3D Game Maker. I'm not sure if a software like that exists.

Also, I agree that 2 weeks is rushed, but I cannot really do longer since this is part of a bigger camp.

I will checkout Processing, it looks interesting. Also, FPS Maker looks good, but since this is part of a bigger camp that includes kids and teens aged 7-17, guns and most realistic weapons are out of the question. I could do with cartoony weapon that shoots carrots and a huge Lollypop as a melee weapon, but, it's going to be limited. Playmaker looks good too, I'm not sure how big Unity is though. Like I said, I would have a hard time convincing IT to install it, if it is quite big.

Built using the open-source PlayCanvas Engine our developer tools will blow you away.

A full level editor running in your browser, connected in real-time to every other PlayCanvas user.

Jam with your friends, collaborate with your colleages or just build a masterpiece on your own.

PlayCanvas is a free HTML5 game engine.

It apparently does not require any installation, has a in-browser editor with collaborative features.

I say that would be the perfect fit for a 2 week code jam for teens.

Of course, entering "html5 game engine" into the Google search box gives you more options, like Quintus, Phaser, Panda.js and Crafty..

That engine looks really good! I actually never have considered making a game using HTML5. I'll definetely check that one out!

I wish I lived nearby, I would surely volunteer. I am working on a curriculum myself for game programming. Right now I have it at 2 hours for the programming side. I think 1 week is good enough time if the curriculum is focused and clear.

I am using a program called MagicaVoxel that makes 3D voxel models. This makes the modeling phase simple, so that you can get to the programming side sooner.

Sounds like a neat camp.

Thanks for the answer. I'll take a look at MagicaVoxel. 3D modelling did take a huge chunk of time out of the two weeks, minimizing that would really help.