Lily Alone by Jacqueline Wilson
Lily isn't home ALONE - but she sort of wishes she was; looking after her three younger siblings is a lot of responsibility. When Mum goes off on holiday with her new boyfriend and her stepdad fails to show up, Lily is determined to keep the family together and show they can cope without any grown-ups. But taking care of 6-year-old twins, her 3-year-old sister and the family's flat feels overwhelming and Lily is worried that school or social services might discover their situation and break up the family. What could be better than to take all the little ones for a camping adventure in the park? Plenty of space to run about, no carpet to vacuum, and surely no chance anyone will guess they're there . . .