is there any furniture in there that can go or is going to go? i would remove the futon.
if it were just for one bed, i would put the bed where the dresser is (in the first picture) perpendicular to the wall such that there is a window on either side of the bed. I would put the book case on one side of the bed (under a window) and the toy chest on the other (under the other window) as "bed-side tables.'
i would put the dresser on the wall with the third window, likely on the left side (when facing the window).
on the wall with the door, between the door and the radiator, if i were using a crib and my child were sharing this room with an infant, i would put the crib there (between door and radiator).
all along the long wall, i would put the various toys and storage for those.
i love the color.
i would recommend tension rods with basic curtains of any kind, or roller shades that you can draw at night to block the light, but raise during the day to let the light in.