Nana Upstairs and Nana Downstairs - Tomie dePaola
I first read this book back in 2002 when I was still in Kumon and they had this little library so I was all like, yeah sure what the heck.

I think it's safe to say that one of the very first picture books I've read as a child was such a depressing story and it scarred me emotionally for life. Just thinking about this book makes me cry all over again.