The comedian visited Dollywood in his BBC series Rob Brydon's Honky Tonk road trip.
The singer's Imagination Library provides books for children up to age five across the world.
Hoult was announced as Gilderoy Lockhart two weeks ago but has dropped out due to scheduling issues.
A two-day event includes workshops and presentations from authors.
The challenge in Guernsey has a musical theme and encourages young bookworms to read six books.
The city celebrates the first telling of Alice's story every year on the first Saturday in July.
It is Christopher Awdry's measles in the 1942 that led his father to create Thomas the Tank Engine.
The Big Malarkey Festival will see authors, artists and musicians gather at Hull's East Park.
