There are recipes out there for making cake in bread machines. If the model name and number are on your bread machine, you can probably find the manufacturer's instruction book with recipes on the web. My son got an old bread machine at an estate sale and found the recipe booklet that way.
Sounds like you need some no-cook recipes, too. You might be able to find some no cook candies and cookies. For example, there are some that mix together things such as peanut butter, dry milk, powdered sugar and rolled oats.
I think a recipe for a warm spiced cider would work in your coffee pot. Maybe something that uses apple cider, pineapple juice and spices.
And how about an instant cocoa recipe. I think mom-from-missouri posted one here not too long ago. Those are simple. You only need dry milk, cocoa, sugar. Some people put in powdered coffee creamer for richness. But the kids could measure up and mix those things, then use the hot water from the coffee pot to serve. If you have tiny cups, one pot could have enough hot water for the roomful of kids to have a sample.
How old are the kids? A playdough recipe that uses oil, flour, salt, water and food coloring could be great.
In a similar vein, some families will just have made a no-cooking Christmas craft dough that is made solely from powdered cinnamon and applesauce. (I've seen recipes that also call for Elmer's glue in it, but that is not necessary.) the dough turns out amazingly lightweight and airy and you can roll it out and use cookie cutters on it. Then you let it dry. It makes fragrant little ornaments. Ours are freehand cut gingerbread men, but any shape would be satisfying. I made some ten years ago and they are still nice. I think it could also me made into large beads.
And I would say repeat the recipes that the kids liked. Every measuring/cooking experience does not need to be novel. Repetition really drives it home. If kids make a recipe often enough that they feel like it is familiar and "theirs," it adds to their sense of competence and willingness to try similar things now or when they are older. I think there is a lot to be learned from cooking.
How about if you bring some packaged cookies or graham crackers let the kids make buttercream frosting for them. They could first measure out and mix the frosting, then measure up the frosting, one teaspoon for each cookie.
How about something they each take home if they have first brought in an empty plastic bottle? For example, they could make salad dressings from scratch. Could be a simple as vinegar and oil, with some powdered spices.
Could you use any instant mixes? Like--an instant pudding, plus the measured milk? Just stir and serve, no real need to refrigerate.
There could be some other non-food things to measure and make. There are furniture polishes for example that use something like olive oil with a few drops of orange oil.
Or they could make a dry batch of laundry soap. There are some recipes for laundry soap elsewhere on savingadvice.com. Typical ingredients are grated bar hand soap plus washing soda plus borax. All are powdered ingredients. I suppose they could each take home a measured amount of the finished result and get to have their own clothes washed with it.
You could also do plaster of paris art projects. In that case, they need to measure up only water and the plaster powder.
Another non-food fun thing would be homemade "GAK" That uses cornstarch, white glue, and usually food coloring. Fun, and potentially messy, but can also be played with while sealed inside a zipper sandwich bag.
Well, this was fun thinking about.
I'll leave it to you to search for the actual recipes if any of the ideas sound worthwhile.