Sierra cups are a amazing tool for light weight camping. As you can see in the photo they are really just a metal cup. However in backpacking it serves as your cup, bowl and plate. They are light weight and easy to clean. They are also pretty durable so they will take the abuse the boys dish out. The two shown in this picture are, I would venture to guess, around 20 years old. There is one con, they are metal so they can get hot or cold depending not only what you put in them, but also what the temperature is outside.
A true sierra cup is the smaller bowl shaped one on the left side of the photo. The taller one to the right that looks kind of like a metal coffee cup, is not a true sierra cup. However I am showing you both types as either would work. You can find cups like this in a whole array of colors, sizes and shapes. Pick out one that makes sense for what you will be using it for.
Even if you don't go backpacking, a metal cup like this might be something good for your Scouts to have. Something to claim as their own, that will go through there entire Scouting career with them.
At Philmont we had something called the Philmont Swoosh. All you do is put some water in your cup, move the cup around using the water to sort of clean the particles off the inside of it and then drink it. This is because not only did we need every calorie we could get, but water was hard to get. It could take hours on water pump to fill up all the water bottles. Also it made washing up a lot easier, left far less food behind to attract animals into camp. (Of course the swoosh would be done immemorially after eating.) I should note I have heard recently this technique is no longer recommend, but I don't know that for sure.
What kind of cup do you use? How do you wash it out?