PP offered some great tips! Your girls are going to love the room. I had a couple suggestions I haven't seen mentioned yet. For wall art: I love etsy.com for handmade art or budget-friendly photos. I have some great prints for my 2 girls' rooms. They also have vinyl adhesive quotes or you can order your girls' names. They can be pricey, so I ended just hand painting a two-tone pink cherry blossom tree. Not as fancy as this, but decent enough considering it only cost me a few quarts of paint. This decal from easy is $86. For your windows: I agree with the PP worried about window safety. With those windows, I would invest in plantation shutters (too heavy for a 2 or 3 year old to unlock and swing open) or buy a metal window gate to ensure your kids can't open the window. Then you can buy some pretty sheers to soften the look of plantation shutters. I got some from Pottery Barn Kids that are embroidered with pink and green butterflies to cover my daughter's shutters. It offers a light whimsical look. They're both sleeping now so I can't take photos. I can't copy the image here, but I see one on eBay now with lavender butterflies for $35 per 84" panel. Post photos when you finish the playroom!

The metal wire picture hanger is too small for the wall, but I agree adding more white with the other frames might be too much. Maybe swap out one of the white frames for something metallic or pull one of the blues from the bedding.

I was looking for something similar to what we had growing up. There were 6 kids, 3 girls, 3 boys and 3 bedrooms, a girl's room and a boy's room and my parents bedroom. Obviously our bedrooms weren't 10x10, but we needed 3 of everything and the solution was that the wall with our beds had shelving across the entire room and low cabinets beside each bed, one side wall was 3 closets and the other side wall was 3 banks of drawers and a vanity with 3 drawers. Everything was built in so we couldn't move our furniture around, but it was extremely efficient use of space and provided ample storage for all our stuff. The only thing I found was by closet mates and is based on their murphy bed, but it could be a standard bed and have a couple of shelves over the bed. Ours were set up with a reading light over each bed and every night we would go to bed, turn on our reading light, grab a book that was on the shelf next to the bed and read. I miss that light. Worked better than having lamps on side tables. So - here is the picture I found. Hope it provides you with some ideas. This idea wouldn't utilize the dresser, but provides a ton of different types of storage based on your daughter's needs and looks like it is roughly based on a 10x10 space.

This might not be any of my business, but are you fostering or adopting? Part of your post make me think that you are and if so I have been there and done that with a grey room too! I over thought the heck out of it and in the end a friend set me straight. "Get all the basic furniture, add twinkle lights, and get some fun inexpensive bedding." Anything goes with grey. Truly. If this is not your situation, and this kiddo already lives with you, pick out three comforters and ask them to select one. Do they love horses, butterflies, cars? Go with what they like and choose accent colors for objects around the room that coordinate with the bedding.