A child is happily playing on the slide.
A child is playing on the slide
Child is playing in the slide is mentioned in both sentences
exists e1 s1 x1 x2.(n_slide(x2) & a_happily(s1) & Manner(e1,s1) & on(e1,x2) & Actor(e1,x1) & v_play(e1) & n_child(x1))
exists e1 x1 x2.(n_slide(x2) & on(e1,x2) & Actor(e1,x1) & v_play(e1) & n_child(x1))