There are two small children playing in a yard.
A brother and sister play in their back yard.
Just because there are two small children does not mean they are related or brother and sister.
exists p1 x1 e1 s1 x2 x3 x4.((x1 = x2) & in(e1,x4) & n_yard(x4) & Actor(e1,x3) & v_play(e1) & (x2 = x3) & n_child(x2) & a_small(s1) & Theme(s1,x2) & card_eq_2(x2))
exists s1 x1 x2 x3 x4.(a_topic(x1) & in(x1,x4) & n_yard(x4) & a_back(s1) & Theme(s1,x4) & of(x4,x1) & n_thing(x1) & n_play(x1) & of(x1,x3) & n_sister(x3) & of(x1,x2) & n_brother(x2))