The middle boy stops short, the others hurtle:
What bumps, what shrieks, what laughter turning turtle.
Love, racing between us two, has planned
A sudden mischief: shortly he will stand
And we shall shock. We cannot help but fall;
What matter? Why, it will not hurt at all,
Our youth is supple, and the world is sand.
Better our lips should bruise our eyes, than He,
Rude Love, out-run our breath; you pant, and I,
I -- cannot run much farther, mind that we
Both laugh with Love; and having tumbled, try
To go forever children, hand in hand.
The sea is rising ... and the world is sand.
The poem ends with a threat that indicates their childhood is approaching a dangerous end, as implied in ‘the sea is rising’ — and their unstable world is once more described in terms of sand. 
 It is interesting that Owen chooses a nautical metaphor. The British Empire was built on naval superiority, but here it suggests change and insecurity rather than military strength.