A man and a smiling young boy in a float vest are swimming together.
Father and son in the water.
A man and a young boy can be father and son.  In order to be swimming, one must be in the water.
exists e2 e1 p1 s1 x1 x2 x3 x4 x5.(exists s2.(Theme(s2,x1) & a_together(s2)) & Topic(e2,p1) & Actor(e2,x1) & v_swim(e2) & subset_of(x3,x1) & in(x3,x4) & n_vest(x4) & of(x4,x5) & n_float(x5) & n_boy(x3) & a_young(s1) & Theme(s1,x3) & Actor(e1,x3) & v_smile(e1) & subset_of(x2,x1) & n_man(x2))
exists s1 x1 x2 x3.(n_water(x3) & ne_tim_father(x1) & a_topic(s1) & subset_of(x2,s1) & in(x2,x3) & n_son(x2) & subset_of(x1,s1))