Children having a pillow fight.
The children have a pillow fight.
Having is a form of have.  Both have the same meaning however spoken for different points of view.
exists e1 x1 x2 x3.(ne_nam_children(x1) & Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_fight(x2) & of(x2,x3) & n_pillow(x3))
exists e1 x1 x2 x3.(n_child(x1) & Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_fight(x2) & of(x2,x3) & n_pillow(x3))