Luna and the Star Thief. The Puddlebrook Tales, #1

Luna Finch is nine years old, lives in the village of Puddlebrook, and has a very important job: she counts the stars. Every single one. Four thousand, seven hundred and twelve  plus one wobbly one she isn't quite sure about. So when a star goes missing, Luna is the only person in the world who notices. A moonlit map falls from the sky. A talking hedgehog named Pocket Prickle turns up in the Whispering Thickety with a glowing newspaper and three dire warnings.
And Luna - with her endearingly useless owl Waffles clinging to her hair leaps through a magical puddle into the strangest and most wonderful sky she has ever seen. But the adventure waiting for her isn't the one she expected. The Star Thief isn't a monster. He's a small, grey, forgotten Night Watchman named Mister Mither, who once polished stars and tucked them in until centuries of being overlooked turned his sadness into something sharp.
He doesn't want to destroy the wishes he's stolen. He wants to keep them. Because no child has ever wished on him. To save four thousand, seven hundred and twelve stars and the hopes of every child who has quietly stopped believing Luna must do the bravest thing of all: look up at the lonely villain, and make a wish on him instead.