Here is something I don't recall seeing: the whole game is on the move. Mother and son are escaping something, looking for something, looking for a missing person or recreating a journey by someone else. A little bit more headache for you in terms of more scenes to design, though.
My usual tip for new developers: think small. Aggressively reject ideas. It's always better to start a project you can finish, even if it's not super impressive, than despair from and abandon a bloated project.
Good luck!