A man in dark swimming trunks is playing with a boy in red swimming trunks on the beach.
A father and his son are playing on the beach.
A man does not have to be a father.  A boy does not have to be a son.
exists e1 s1 s2 x1 x2 x3 x4 x5 x6 x7.(n_beach(x7) & on(e1,x7) & with(e1,x4) & in(x4,x5) & n_trunk(x5) & of(x5,x6) & n_swimming(x6) & a_red(s2) & Theme(s2,x5) & n_boy(x4) & Actor(e1,x1) & v_play(e1) & in(x1,x2) & n_trunk(x2) & of(x2,x3) & n_swimming(x3) & a_dark(s1) & Theme(s1,x2) & n_man(x1))
exists e1 x1 x2 x3 x4.(n_beach(x4) & on(e1,x4) & Actor(e1,x1) & v_play(e1) & subset_of(x3,x1) & n_son(x3) & of(x3,x2) & n_male(x2) & subset_of(x2,x1) & n_father(x2))