I have really enjoyed looking at all of your colored pencil pieces, and this one is really beautiful! I love your style. It is so soft and so gentle, and perfect for the subjects you chose. I especially like the treatment of the curly hair, and their eyes are so big and innocent; just great!
I think a bit of a background could actually be very nice and really help to pop those girls out, as long as it is not very detailed. Maybe just impressions of the background objects in a varied shape sort of tonal manner. Hope that makes some sort of sense.
p. s. I really love your piece with the girls at the pond/lake with the ducks! It is so GREAT!