Close friends with a neighbour, is a single mum to 8 year old DD so I've offered to look after her a few times whilst she's had meetings, appointments and so on. So a few times she's been in a rush, needed to be somewhere urgently and has dropped her DD off at mine which I'm fine with. But nowadays it seems I'm looking after her child at least a few hours a week. I do want to help her out as I'm her friend but I have 3 kids myself. A few weeks ago her DD knocks on my door about 20 minutes after getting home from picking DS up and says her mum isn't home and she doesn't know where she is. She turns up half an hour later saying she completely forgot. I know i need to put a stop to this but i feel bad, she isn't in contact with any of her family, doesn't have many other friends. I'm just not sure how to talk to her about this