12 hours is a very long day. I would suggest shortening the day to something more manageable for yourself and your family.
I suggest making a nap schedule, so that most children are napping at the same time. You need a break too and this rest time is also a great time to tidy up somethings.
I agree with the above post. You are providing childcare, you are not a restaurant. Get the children to help with the menus and serve what is on your menu for the day, they decide if they will eat or not.
Any food prep that can be done early, I do on Sunday. Daily meals I prep the evening before so everything is set and ready for when I need to cook.
Can you engage the children and see what their interests are? What kinds of activities do you offer?