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!

Perhaps a large round table might mean a rug is not at all necessary. It could be a metal tray table, or carved wood like Rebecca Mitchell Interiors illustrates. Ideas also to consider, using multiple tables can be found at http://www.houzz.com/multiple-coffee-tables. I also agree with comments above that some color is needed on the walls. You could then hang round mirrors, or an unusual curved shape like RMI shows above.

Overallshot

you could always use any glass top table with steel frame and put a matt finished steel tray arranged with some metallic miniatures or candle stand or spray paint some wooden table with metallic paint and give an oxidised look.