I would not buy muffins like this.
I like to bake, so I always have ingredients at the ready. Also my kids are older, and they're past the stage where getting them to eat veggies is a problem. So, I'm not looking at muffins as a way of sneaking something healthy into them. If I'm making muffins, I'm intentionally making a snack food, not a health food.
Also, I'd be surprised if you could make them cheap and convenient enough to get people to buy them and still clear a profit.
However, judging by the number of PTA fundraiser flyers I've seen that revolve around ready-made foods, I'm betting that other people might be into this. You may want to repost on the preschool board. That's the age range when getting kids to eat veggies is the biggest drag. I would think they're more likely than a parent of a school-aged kid to be into something like this.