I recently read The City of Ember by Jeanne DuPrau.

The city of Ember is running out of supply.Fast.That's why

all twelve year old's must work Lina Mayfleet desperately wants to be a messenger job a and gets the Pipeworks job.When her fellow classmate,Doon,gets the messenger job,they both trade,because they both highly dislike their jobs.While at home,Lina discovers a mysterious looking box

witha note inside.But before she could read it,her baby sister,Poppy,chews it up,leaving only a few letters.But with a little help from her friends she figures out the way out is through the pipeworks.While she was scoping it out,she discovered that the mayor was hogging all the needed supply!Later,when they go back to the pipeworks,they find boats and candles.They float a boat down the river,were they discover the haven.