A man drives a truck while a child sits on his lap and steers.
A small boy sits on his dad's lap and steers a truck.
Just because a child sits on a man's lap does not mean it is a small boy or it's their dad's lap.
exists e1 p1 x1 x2 x4 x5 x6.(exists e2 x3.(on(e2,x4) & Actor(e2,x3) & v_sit(e2) & n_child(x3)) & n_steer(x6) & n_lap(x5) & subset_of(x6,x4) & subset_of(x5,x4) & of(x4,x1) & n_male(x1) & while(e1,p1) & Theme(e1,x2) & Actor(e1,x1) & v_drive(e1) & n_truck(x2) & n_man(x1))
exists e1 e2 s1 s2 x1 x2 x3 x4 x5.(Theme(e2,x5) & Actor(e2,x4) & v_steer(e2) & n_truck(x5) & n_boy(x4) & a_small(s2) & Theme(s2,x4) & on(e1,x3) & n_lap(x3) & of(x3,x2) & n_dad(x2) & of(x2,x1) & n_male(x1) & Actor(e1,x1) & v_sit(e1) & n_boy(x1) & a_small(s1) & Theme(s1,x1))