What a fun space! Love the pillows...I agree with above, lower all the frames, but not so low little ones can reach. The art should fall at eye level about 5'4" for walls and for behind the sofa not more than 12" above it. Then keep the width about 5" inside the sofa length on each side. Your frames are small so you need the close together for impact. I would start with some pretty curtains for the door and large window and then a simple Roman shade for the small window- since your girls play there you don't want anything they will grab hold of. http://www.houzz.com/ideabooks/query/how-to-hang-a-photo-gallery

Here it is (but I'm guessing it will be available from more places): http://muralunique.com/index.php?route=product/product&path=53_56_77&product_id=937&sort=p.price&order=DESC

If you think hitting the lamps could be an issue, just move them a bit and add some low accessories (opposite sides to pic below). It's better to have a bit larger lamps and with your ceiling height anything shorter would look skimpy and they don't overwhelm the bedside tables once you balance with something above the bed. Just a thought...if you accessorize your bedding with some soft colors, they will also help to compliment the glass and crystal. You could even change the hardware to a silver.

I think something like this would be perfect for what you're trying to do! Except, you don't have the earth to help you out. Potted plants should be fine.