Lots of ideas....couldn't resist adding my two cents. i copied your photos and did a little cut and paste- it's messy, but hopefully gets the main idea across. i'd put your sofa in front of the large book case, chair by the fireplace, tv on the stand on the wall opposite the fireplace - so you can either look at the fire or the tv. Someone suggested using frames of one color for your photos - an inexpensive way to do that would be to spray paint them all a dark color-black goes with everything. Since your shelves are a medium tone wood, display things that are dark or light so that they contrast against the wood. Limiting your display items pallette to a few values usually helps to unify things. (I think that's why so many people want to paint the shelves or put inserts in the back to help your nice things read more clearly...some get lost). If you want to "splurge" -you may consider having a carpenter make a few solid tall cabinet doors to provide a visual break in the shelving. I'm showing 3 doors - 1 on the right side of the fireplace and 2 on the left to leave two open vertical shelves for display on each side - with things arranged to frame the fireplace as the focal point. To add some height to your big vases, consider stacking some books beneath them. Enjoy experimenting untill you get something you're happy with - good luck!

Simplify is always a good strategy with play rooms. The temptation to cover the walls with artwork and posters can add to the visual clutter. I would suggest a larger area rug to ground the space and create a soft place for playing on the floor. A medium colour with a fleck from other hues in the curtains and upholstery will help hide dirt and lint. I think you could definitely cozy it up with a warm wall colour to unify the space. Lastly, closed storage for the toys goes a long way to creating order from the chaos. You will have a lovely space the children enjoy and you find restful.

For what it is worth, I don't generally recommend leaning mirrors over fireplaces. They may reflect a chandelier, but what they primarily reflect is the ceiling. Not attractive in most instances. Just food for thought... The above recommendations are both terrific. Be sure they are scale appropriate.

I would also definitely go white if the windows are on the green wall. Will be much more natural to tie the accent wall with the stark wht contrasting walls. Always a very chic contemporary look. Also very relaxing as opposed to the treatments standing out when you already have your standout feature- the green accent wall. Great white bed you ordered! Then I love all the blue/green/ silver accent advice. I did a similar room in purples/greys/ whites and we used great posted prints of florals with a little oriental flair in nice big mats w frames. You could do florals or nice big botanicals in greens would be very fresh and modern!! White or silver frames or maybe even the shock of black would be cool.