A group of boys play in front of camera.
The children are playing.
children are playing is a more generic way of talking about the boys playing, without saying where they're playing.
exists e1 x1 x2 x3 x4.(in(e1,x3) & of(x3,x4) & n_camera(x4) & n_front(x3) & Actor(e1,x1) & v_play(e1) & of(x1,x2) & n_boy(x2) & n_group(x1))
exists e1 x1.(n_child(x1) & Actor(e1,x1) & v_play(e1))