Easy sweet recipe needed for school baking

I like baking. I do. However school baking tends to be due on inconvient days like today, Wednesday requiring late nights or organisation like I did this week, bake weekend, freeze cupcakes, ice last night. Icing cupcakes just before bed is not an ideal preparation for children to calm down and go to sleep though I tell you.
More baking is due for the athletics carnival next Thurday. I know I could stop by the supermarket on the way home and buy some cupcakes but really it's easier to make them than take 3 tired kids into a supermarket at 6pm. Also, the kids love to help. So it's a good family activity.
I need a new recipe. I'm thinking a slice which doesn't involve the individual preparing of each one. One slice, slap it in one container, bake and cut. Preferably one that freezes well. Hit me up.