I think that you need mostly white, but something in a print that incorporates your colors. Perhaps pillow slips or at least a mostly pea green painting/poster/wall-hanging that also has some brown, perhaps in the frame. You could also do a stencil on the pink wall using the green paint, some white, and some brown. How about a nice tree branch? You can also buy vinyl decals from Etsy or other places--not sure that you could get pea green, but brown and white should be available.

Its a really lovely room! what a great place for kids to share. I like kids sharing rooms. I think you need another colour to tie it together. I would suggest a blue tone.... teal, navy blue, duck egg blue. to tie it together. Its a little to pale and looks sparse, but actually isn't. I would leave everything exactly as is, BUT, paint the back wall behind the bed teal and find a simple navy blue wall decal that is fun and kid- like maybe one with a sillouette of a boy and girl playing. I would paint the wall behind the sofa duck egg blue. Then I think it would suit both kids more and look more kid friendly. the blues will balance the pink and cream, but because you have a pale carpet i don't think it will look too dark. don't worry about making it totally kid like, its a room they will grow with, not a kindergarten, and it also needs to peaceful and restful for sleeping. besides with their art on the walls and bright toys everywhere it soon looks bright and kid like. Good luck!

Personally I wouldn't paint the door and window but if you don't like it I'd paint it a soft white. I'd go for a pale but warm grey on the wall with full length curtains to match and add your favourite colour/s in accessories. If you're not keen on pale grey I'd go for an off white with a yellow undertone (farrow and ball do some great colours which would work) IF you can get an upholstered bed I would but if not add cushions and a throw. I'd also add a rug under the bed for softness. Do you have a ceiling light? A mirror and some great art would complete it. I wouldn't add a curtain to the wardrobes, I don't think it needs it

My first question will be: what is the utilities of this room? Who live in it? Age, gender? Is this room oriented by the North or South? East or West? What do you want to feel in this room? Serenety? Concentration? Spirituality? Energy? After all this answer it will be easier to help you. :)