Back in the 80's, I read a novel about a girl named Jamie whose father was a maintenance worker for an underground bunker reserved for important people (president, Congress, scientists, etc) should there be a catastrophe (nuclear winter, etc).
Earth had made contact with an alien planet and was engaged in a territorial dispute over a planet both groups wanted to colonize. Jamie and her younger brother accompany her father on one of the routine facility checks of the bunker, and while they're there, the alien group attacks Earth and wipes out human beings.
Jamie, her brother, and her father seem to be the only people left on Earth. Dad spirals into a deep depression, Jamie and her brother manage by riding the quad vehicles through the corridors of the facility, eating canned peaches, and using the radio communications system in the bunker -- ultimately it's up to the kids to keep up the search for survivors.
They make contact with some people who were in a submarine at the time of the attack, and they begin to realize that anyone who was underground or underwater (deep) at the time of the attack would have survived. They get dad out of bed with this information, and ultimately they begin contacting others.
There's an epilogue in the book in which Jamie's great-granddaughter is living once again above ground, rebuilding human society.
I really liked this book, but I do not remember the title or the author.