A children's choir are in blue and red robes.
A children's choir is singing.
The children's choir is not necessarily singing. They could be waiting for the vocals to become necessary.
exists p1 x1 x2.(exists s1 s2 x3.(in(x2,x3) & n_robe(x3) & a_red(s2) & Theme(s2,x3) & a_blue(s1) & Theme(s1,x3)) & n_choir(x2) & of(x2,x1) & n_child(x1))
exists e1 x1 x2.(Actor(e1,x2) & v_sing(e1) & n_choir(x2) & of(x2,x1) & n_child(x1))