Young children on a sled are being pulled through the snow.
A teenager is sledding down a steep hill by himself.
Children on a sled means more than one child, and not a sole teenager. The children are being pulled by someone else, so a child isn't by himself.
exists e1 s1 x1 x2 x3.(n_snow(x3) & through(e1,x3) & Theme(e1,x1) & v_pull(e1) & on(x1,x2) & n_sled(x2) & n_child(x1) & a_young(s1) & Theme(s1,x1))
exists e1 s1 s2 x1 x2.(by(e1,x1) & n_male(x1) & a_down(s2) & Manner(e1,s2) & Theme(e1,x2) & Actor(e1,x1) & v_sled(e1) & n_hill(x2) & a_steep(s1) & Theme(s1,x2) & n_teenager(x1))