The Blue Book of Nebo

Dylan was six when The End came. 
Now he is fourteen. Since the disaster that changed everything, Dylan and his mam have survived in their isolated hilltop house above the village of Nebo in north-west Wales, learning new skills and returning to old ways of living. They trap rabbits, tend the vegetable garden, and take turns caring for Dylan's little sister, Mona.
Dylan does not remember the time before they were alone, before the electricity went off for good, before the "normal" twenty-first century world disappeared.
His mother, Rowenna, has given him a simple task: to write in a journal, the book now in your hands. 
When, one night, Dylan asks his mam to write too--the story of The End and of the life before that he cannot remember--the Blue Book of Nebo is created.
"We've agreed not to read what the other has written, just in case," Dylan writes. "In case of what, I'm not sure."
Together, they take turns writing their histories, what they remember, and what they can piece together of the outside world--and the secrets they have kept from each other for the past eight years.
What brought The End?
What was life like before?
Where did Dylan's baby sister Mona come from?