The Gruffalo
Julia Donaldson & Axel Scheffler
The best one for this. The monster is real, and a mouse beats it by thinking.
Books for kids who are scared of monsters and the dark
Hiding monsters from a scared kid rarely helps. What works is a story where a monster turns up and the small person comes out on top.
Room on the Broom
Julia Donaldson & Axel Scheffler
A dragon arrives and friends scare it away. Being together is the weapon.
Where the Wild Things Are
Maurice Sendak
Max tames the monsters by staring into their eyes. A big scene for a small kid.
Owl Babies
Martin Waddell & Patrick Benson
For fear of the dark itself: three owls in the night, and the morning-after relief.