Scratch

Sounds interesting, a bit like my Easter Egg Hunt project (on the Scratch 2.0 website) but with a timer. However, I'm not sure clicking around a room is the most exciting thing ever. At the very least, you could make it so that, say, the history room is cluttered with pots and helmets from the Roman era and such so it is very cluttered and the specific object being searched for is very hard to find. You could also add special parts like somebody taking an object and you have to take part in a little race game to get it, but this could take a while. Another idea is to make the game a platformer. Say, you start in the Maths room, you have to jump over books and avoid spinning + symbols (I know, weird) to reach the object, then you go onto the next room which has the theme of a different subject. You basically must see how many levels you can complete in the given time. The downside of this is that it would require quite a bit of knowledge on Broadcasts and Variables, which childeren of that age do not know about. Actually, the idea as a whole would require broadcasts and variables, so I just hope that they can figure it out with some help.

I hope that these suggestions and ideas are helpful. This does seem like quite the project for 25 minutes, as I would imagine something like a racing game would fit the time span better. However, if you can sit down and make the game yourself in 25 minutes, then maybe you can show the childeren how in even less. Good luck! Let me know what you think of all of this.

A racing game shouldn't be too hard. You could make them all make a simple multiplayer racing game, and have those that find it easy add fun bits like speed boosts, power ups, things like that. All that they would need to do would be to draw a race track background, add 2 driving cars and their scripts and make some scripts so that if they touch the green grass colour then they lose.