I think this is a great idea Nadine! Packaging it for different people would be really useful. In a class exercise, we had to pick a random partner and feed each other. You don't realize how intimate it is until you're the one being fed! Simulating what its like to be taken care of would be super useful for caregivers.
I like the idea of people benefiting from providing service to others. It sounds to me like there might be different levels of function that we are identifying - there is a big space between early retirement, looking for new experiences, still living independently and people living in nursing homes, needing lots of care and supervision. I think that maybe one could help facilitate the other in the classroom, like if there were more able bodied elders around, it would be easier for elders who need more help to interact productively with children.
I agree that 6-7 year olds would be a great age to start working out the details of how to bring children and the elderly together, but I would also encourage including younger children eventually as well. 3-6 year olds can be incredibly empathic and when given the right kind of instruction, they can be very mindful of the needs of others. Plus, there is so much joy in just being with children that age, I think it could bring a lot of comfort.