A child in orange poses in the snow riding a blue sled.
A child is posing on a blue shed.
"Poses" is to tell what he does now. "Posing" is to emphasize what he does right now. Riding a sled is to sit on the sled, so the child is "on" the sled.  (Typo on your sentence 2: sled not shed)
exists e1 s1 x1 x2 x3 x4 x5 x6.(n_snow(x4) & a_topic(x1) & in(x1,x2) & in(x2,x4) & Theme(e1,x6) & Actor(e1,x5) & v_ride(e1) & n_sled(x6) & a_blue(s1) & Theme(s1,x6) & (x4 = x5) & n_pose(x2) & of(x2,x3) & n_orange(x3) & n_child(x1))
exists e2 e1 x1 x2 x3.(on(e1,x2) & Theme(e2,x3) & v_shed(e2) & (x2 = x3) & n_blue(x2) & Actor(e1,x1) & v_pose(e1) & n_child(x1))