Who or what is the children that Shel talks about in the second last line?

Where the Sidewalk Ends by Shel Silverstein



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

To the place where the sidewalk ends.



Yes we'll walk with a walk that is measured and slow,

And we'll go where the chalk-white arrows go,

For the children, they mark, and the children, they know

The place where the sidewalk ends.

Who or what is the children that Shel talks about in the second last line?
They are the children who are currently children, and they are the children all adults used to be.