It is a day to celebrate books and reading and school children typically dress up as their favourite book character.
Have a look at some of the children in Derry dressed up today.
9. Charlie and the Chocolate Factory
Fletcher and the Chocolate Factory
10. Gangsta Granny
Gangsta Granny
11. Flip Flap Farm
Jacob as Peep from Flip Flap Farm.
12. Billionaire Boy
Joe dressed as Billionaire Boy