Toddler sits on a pile of rocks.
The toddler is playing in the rock garden.
Just because the toddler is sitting on rocks, it doesn't mean he is playing.  Also rocks can be found anywhere, not necessarily in a rock garden.
exists e1 x1 x2 x3.(ne_nam_toddler(x1) & on(e1,x2) & of(x2,x3) & n_rock(x3) & n_pile(x2) & Actor(e1,x1) & v_sit(e1))
exists e1 x1 x2 x3.(n_garden(x2) & of(x2,x3) & n_rock(x3) & n_toddler(x1) & in(e1,x2) & Actor(e1,x1) & v_play(e1))