The children played on the four wheeler in the field.
The children are playing.
Playing is a rephrasing of played.
exists e1 x1 x2 x3.(n_field(x3) & n_wheeler(x2) & card_eq_4(x2) & n_child(x1) & on(e1,x2) & in(x2,x3) & Actor(e1,x1) & v_play(e1))
exists e1 x1.(n_child(x1) & Actor(e1,x1) & v_play(e1))