The little boy lost in the lonely fen,
Led by the wand'ring light,
Began to cry; but God, ever nigh,
Appear'd like his father, in white.
Blake chose chose to set his poem in ‘the lonely fen’, significantly because fenlands are swampy and can be treacherous at night. The Fens of East Anglia regularly take lives through drowning. 
 The simple, unadorned introduction leads the reader into the more complex, symbolic lines. The little boy is representative of vulnerable childhood as well as innocent but misguided humankind.
The Little Boy Found Songs of Innocence