There is a place where the sidewalk ends
And before the street begins,
And there the grass grows soft and white,
And there the sun burns crimson bright,
And there the moon-bird rests from his flight
To cool in the peppermint wind.
Let us leave this place where the smoke blows black
And the dark street winds and bends,
Past the pits where the asphalt flowers grow
We shall walk with a walk that is measured and slow,
And watch where the chalk-white arrows go
Although it’s “just a kids' poem,” “Where the Sidewalk Ends” echoes a classic scenario from  Romantic poetry,  in which the poet/speaker retreats from the busy, noisy, worldly city into the quiet, innocent, spiritually renewing countryside. 
 Here’s Wordsworth (a poet obsessed with childhood innocence) in “Tintern Abbey”: 
 If this Be but a vain belief, yet, oh! how oft– In darkness and amid the many shapes Of joyless daylight; when the fretful stir Unprofitable, and the fever of the world, Have hung upon the beatings of my heart– How oft, in spirit, have I turned to thee, O sylvan Wye! thou wanderer thro' the woods, How often has my spirit turned to thee! 
 Here’s W. B. Yeats in “The Lake Isle of Innisfree”: 
 I will arise and go now, for always night and day I hear lake water lapping with low sounds by the shore; While I stand on the roadway, or on the pavements gray, I hear it in the deep heart’s core. 
 You could argue that Silverstein’s speaker is retreating more to the ‘burbs than to the countryside per se, but the “place where the sidewalk ends” is nonetheless full of natural beauty: grass, sun, birds.
Where the Sidewalk Ends