This is about a discussion in Gimp Users:
www.flickr.com/groups/gimpusers/discuss/72157629887224116/
The first thing was to remove two grass blades that were partially hiding the kid's face. As they were very blurry and let the face visible through some sort of green filter, I tried to use layers that corrected the color but kept the real image data visible instead of cloning the surrounding parts.
I added several layers, used as "color filters", masked them in black and painted the mask in white to remove the grass as if it was a green cast. There were several layers as several layer modes were needed (especially for the right part of the mouth which lacked contrast and saturation => overlay layer).
The process was not as efficient for the cloth, and I had to clone, for I didn't get exactly the right color.