the young children are petting a piglet
A pig isn't being petted.
If a pig isn't being petted then the children cannot be petting a piglet.
exists e1 s1 x1 x2.(n_child(x1) & a_young(s1) & Theme(s1,x1) & Theme(e1,x2) & Actor(e1,x1) & v_pet(e1) & n_piglet(x2))
exists x1.(-exists e1.(Theme(e1,x1) & v_pet(e1)) & n_pig(x1))