What if you could go into a single store, or go online, answer short list of questions about each of your kids, and have school supplies shipped to your house the week before classes?
Would you pay $40-50 per child to know that they had everything they need for chemistry class, art, math, and history and that you wouldn't have to spend your entire Saturday driving around?
You might have to do some serious research on the different schools and teachers, but you could also start with one school. A single school with 1,000 kids is still profitable. If you managed to get 10% of the school to use your service, that's $4,000 gross revenue. If half of that is profit, you just made $2,000 for packaging school supplies for 100 people.
I give this idea a 6 out of 10 so far. It has room to improve still. It's missing something I think, but it's a start.