This is a great idea! It has potential and I believe will be successful as grannies play a very important role in children life. As from my own experience, a grandmother/father is always on your side and can teach you many useful things that you can carry on your entire life. I also think that children will attend the lessons with patience and interest, because the grandparents have their own pleasant way to explain things. Sometimes, parents in poor communities, might not be that patient with children as they always think about the problems they have regarding living. I would say grandparents are the best fit to teach children. Good luck with your project!