The tone is lighter than Ben Jonson's elegy 'On My First Son'. Kennedy's poems are always full of richly playful elements.
I found analysis of the poem: Blog of Poet, Translator, Essayist A. M. Juster.
for a child who skipped rope
by X. J. Kennedy
Here lies resting, out of breath,
Out of turns, Elizabeth
Whose quicksilver toes not quite
Cleared the whirring edge of night.
Earth whose circles round us skim
Till they catch the lightest limb,
Shelter now Elizabeth
And for her sake trip up death.