Final Answer:
Yes both The Little Boy Lost and The Little Boy Found contain sonnets of four lines.
Step-by-step explanation:
In both poems William Blake employs the sonnet form which consists of 14 lines. Each sonnet is divided into two parts with the first part having eight lines known as the octave and the second part having six lines known as the sestet. However it seems there might be a confusion in the question as it mentions sonatas which typically refer to musical compositions whereas sonnets are the appropriate term for the structure of these poems.
The Little Boy Lost and The Little Boy Found are part of William Blake's collection Songs of Innocence and Experience. The poems share thematic elements and explore the loss and rediscovery of innocence. Blake's use of the sonnet form provides a structured framework for conveying his profound reflections on the human condition. The consistent use of four-line stanzas in each sonnet contributes to the overall symmetry and balance of the poems enhancing their aesthetic appeal and reinforcing the thematic unity within each work.
In summary the poems in question are sonnets not sonatas and both adhere to a fourine stanza structure within the broader sonnet form. This deliberate choice in structure reflects Blake's artistic intent as he weaves his narrative and thematic concerns with a careful balance of form and content.