When they're running with the wind in their faces and the sun on their backs, or stepping barefoot onto cool, green grass.
( ( When ( they ( 're ( ( ( ( running ( with ( ( ( ( the wind ) ( in ( their faces ) ) ) and ) ( ( the sun ) ( on ( their backs ) ) ) ) ) ) , ) or ) stepping ) ) ) ) ( ( barefoot ( onto ( cool ( , ( green grass ) ) ) ) ) . ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (PRP they)) (VP (VBP 're) (VP (VP (VBG running) (PP (IN with) (NP (NP (NP (DT the) (NN wind)) (PP (IN in) (NP (PRP$ their) (NNS faces)))) (CC and) (NP (NP (DT the) (NN sun)) (PP (IN on) (NP (PRP$ their) (NNS backs))))))) (, ,) (CC or) (VP (VBG stepping)))))) (VP (VBP barefoot) (PP (IN onto) (NP (JJ cool) (, ,) (JJ green) (NN grass)))) (. .)))
They are running barefoot in the grass. 
( They ( ( are ( running ( barefoot ( in ( the grass ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (VP (VBG running) (NP (NP (NN barefoot)) (PP (IN in) (NP (DT the) (NN grass)))))) (. .)))