Respectfully Quoted: A Dictionary of Quotations. 1989.
Francis Thompson (18591907)
Know you what it is to be a child? It is to be something very different from the man of to-day. It is to have a spirit yet streaming from the waters of baptism; it is to believe in love, to believe in loveliness, to believe in belief; it is to be so little that the elves can reach to whisper in your ear; it is to turn pumpkins into coaches, and mice into horses, lowness into loftiness, and nothing into everything, for each child has its fairy godmother in its own soul; it is to live in a nutshell and to count yourself the king of infinite space; it is To see a world in a grain of sand, And a Heaven in a wild flower, Hold infinity in the palm of your hand, And eternity in an hour; it is to know not as yet that you are under sentence of life, nor petition that it be commuted into death.
FRANCIS THOMPSON, Shelley, The Works of Francis Thompson, vol. 3, pp. 78 (1913).
The poem quoted is Auguries of Innocence by William Blake.