irresponsible mothers

My neighbour has two young children, their father doesn't live with them - not his choice I believe. She (mother) frequently goes off for long weekends and childcare seems rather random. Sometimes a young woman is there with them, sometimes they got to stay elswhere, they seem to stay with their father at least once each weekend. This mother isn't there sometimes when the children are brought home and I have seen them left with a neighbour. It seems to me that these little girls are just a meal-ticket for a mummy who wants to go out and have fun. How can she be scared into taking better care and not 'dumping' them on anyone who will have them. i know for a fact that today she suddenly decided to stay away an extra night and I saw their father having to take them to stay with his new girlfriend. What can I do?