The child playing on the deck has a red bucket on their head.
The child's sister dumped a bucket of sand on his head.
There is no indication that the child has a sister. Having a bucket of sand dumped on his head is not a form of playing. The child might not be male so it would not reference his head.
exists e1 s1 x1 x2 x3 x4 x5.(n_head(x5) & of(x5,x1) & n_thing(x1) & n_deck(x3) & n_playing(x1) & of(x1,x2) & n_child(x2) & Theme(e1,x4) & Actor(e1,x1) & v_have(e1) & on(x4,x5) & n_bucket(x4) & a_red(s1) & Theme(s1,x4) & on(x1,x3))
exists e1 x1 x2 x3 x4 x5.(n_head(x5) & of(x5,x1) & n_male(x1) & n_sister(x2) & of(x2,x1) & n_child(x1) & on(e1,x5) & Theme(e1,x3) & Actor(e1,x2) & v_dump(e1) & of(x3,x4) & n_sand(x4) & n_bucket(x3))