There is! With the newest version ( 0.7 ) get persistent saves. The app asks for permissions when you start it the first time and when you save now you will keep your savegames even when you uninstall the app. They are stored in /Android/data/RenPy/MyNewFamily-somenumbers. Keep in mind that some cleaning apps tend to delete these savegames though. Before 0.7 you had to manually backup before each update but now you don't have to anymore.