How can i get my mum to take more care of my sister?
Try talking to her, your father, a councler, etc., but if that doesnt work… Make plans with your friends all the time so when she asks you to babysit you can say “no i have plans sorry”. Let your little sister distroy something while she is in your care, let her draw on the walls with crayons. Your mom won’t make you watch her then! *I am assuming you are telling the truth that is why I am giving you this advice. But if your mom wants you to babysit once a week for a few hours then you should not be complaning. But if it is as serious as an issue as you make it seem then you should do something about it. It is her child, not yours.
