What's the Name of That Book??? discussion

So I saw this book in a Barns and Noble during the summer of 2013. I read the first few pages of it and it focuses on a teenage girl. She gets home from school one day and her parents dont return home, no one answers her calls, the news is really bad or something like that. A part I particularly remember is, due to her being so distraught and panicked, she eats a bunch of ice cream and then throws it all up. I know that doesnt really give you a lot to work with, sorry. Another thing I think I remember is she saves this little kid? (The kid was very young, around 2 or 3 maybe?). I think I remember it being an alien invasion apocalypse type of thing.
Sorry there's not a whole lot here to work with, thanks in advance for any help you can give me!

Is it In the After?
It fits a lot of what you mention.

Omg yes that's the one!!! Thanks so much! Have you read it before?

Yeps! I read it last summer and I liked it.

You're welcome!