Was thinking along the lines of mamaof4. It almost sounds like they want to get involved somehow. Maybe their own grandchildren live far away or they don't have any and wish they did and would love to come and hang out with you and the kids - grandma's make great reading and baking partners.

I like the idea of introducing the children to them in some way. Start by only introducing your own children as people who also live in the neighbourhood. Then mention that the other 5 children are only with you during the day while their parents are at work and somehow work into the conversation what the legal limits are for daycare, etc.