These people are waiting in line on a staircase.
Parents wait in line on a staircase.
We have no idea if the people are parents, they could be anyone.
exists e1 x1 x2 x3.(n_people(x1) & on(e1,x3) & n_staircase(x3) & in(e1,x2) & n_line(x2) & Actor(e1,x1) & v_wait(e1))
exists e1 x1 x2 x3.(on(e1,x3) & n_staircase(x3) & in(e1,x2) & n_line(x2) & Actor(e1,x1) & v_wait(e1) & n_parent(x1))