Animal Crossing how do you get a mum

The aim of the game is moving out of your parents house and living on your own so really you already have a mum who sometimes sends you letters in the post. Hope this helps xx Or basicaly its just that you are leaveing to explore the world and every now and then your mum will send you a letter telling you that she misses you and blah blah blah but you cant send her leters for some reason?????