Father is pushing his son on the track.
This is the boys first time on a tricycle.
Pushing ones son on a track does not imply that it is the first time this has happened.  Tricycles are not often found on tracks.
exists e1 x1 x2 x3.(n_track(x3) & n_son(x2) & of(x2,x1) & n_male(x1) & ne_nam_father(x1) & on(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_push(e1))
exists p1 s1 x1 x2 x3.(n_time(x2) & a_first(s1) & Theme(s1,x2) & of(x2,x3) & n_boy(x3) & n_thing(x1) & exists x4.((x1 = x2) & on(x2,x4) & n_tricycle(x4)))