I like the IKEA Cecilia bird fabric that Catherine suggested a LOT. It even comes in a green colorway that might be very similar to Anand's actual walls -- would need to see in person to be sure. Take a look:
Charming, whimsical, and suggesting something that a child might carry around in his sketchbook. If the child had more artistic talent than I do, anyway.
On the other hand, people don't seem nearly as excited about patterned curtains as I am. (People including Kevin.) Maybe it makes more sense to just do a solid color, and bring in pattern on Anand's bedding and maybe his rug. We'll see. There's a big expanse of white on his ceiling, so I do want to bring some pattern in somewhere.
If I do solid curtains -- what color? Off-white (too much with the ceiling, or perfect complement to brighten the room)? Medium blue (a safe, sky-like choice)? Or be bold and go with a purple picked up from the rim of those knobs?