Final answer:
William Blake defined innocence as childlike purity.
Step-by-step explanation:
In his poetry, William Blake defined innocence as b) Childlike purity. He believed that innocence was a state of being untainted by the world's corrupting influences, like a child before they are exposed to sin or evil. This is evident in his collection of poems called 'Songs of Innocence', where he depicts the purity and beauty of childhood.