How about operating a day care center to watch customers kids while they shop at the store? Of course, put an hour limit on the service.
Some Malls have services for watching children while the parent's shop, but it should not be individual stores.
Lawsuit city. Will not happen.
They could take a page from McDonalds and erect fairly large playscapes for kids between roughly 6-12. It would keep them occupied while parents shop. If they are shooting for the 25-45 demographic, they are shooting for people with children.
Cost, liability, responsibility. Generally people shouldn't and wouldn't leave their children with persons they don't know. Nice thought though.