Two black-haired boys are squatting on the ground while holding handfuls of marbles.
Two boys on the ground holding marbles.
on the ground may mean laying on the ground and not squatting.
exists e2 e1 s1 x1 x2 x3 x4.(n_ground(x2) & while(e1,e2) & Theme(e2,x3) & Actor(e2,x1) & v_hold(e2) & of(x3,x4) & n_marble(x4) & n_handful(x3) & on(e1,x2) & Actor(e1,x1) & v_squat(e1) & n_boy(x1) & a_black-haired(s1) & Theme(s1,x1) & card_eq_2(x1))
exists e1 x1 x2 x3 x4.(n_ground(x2) & a_topic(x1) & on(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_hold(e1) & n_marble(x4) & (x2 = x3) & n_boy(x1) & card_eq_2(x1))