What might be the poet's purpose in this poem?

The Little Boy Lost
by William Blake

Father, father, where are you going?
O do not walk so fast!
Speak, father, speak to your little boy,
Or else I shall be lost.

The night was dark, no father was there,
The child was wet with dew;
The mire was deep, and the child did weep,
And away the vapor flew

to warn
to explain
to interpret
to frighten