Starvation isn't the only cause of greenish stools. Some forms of diarrhea can also cause a similar thing. This is because, in diarrheal diseases, there is intestinal hurry, with drastic reduction of intestinal transit time. In simple language, faeces moves through quickly, giving little time for convertion of the greenish colored Bilirubin to the brownish Stercobilin.
The first stool every baby passes, meconium, is also greenish in color, for the obvious reason that he/she is yet to feed.
Occasional passage of a greenish stool, especially if bulky, and the child is not losing weight, may also be normal.
Lactose intolerance, and milk allergy, may also cause it. In these cases, the child may be fussy, and irritable as well. In the former, there may also be bloating, and excessive passage of gas. .Greenish colored stools, the so called "starvation stools," could be an indicator that a child is not being fed well; that he is starving.
This is so as, suboptimal feeding makes small volumes of food materials to be present in the intestine. Most of these would be absorbed by the body, and what would be present at the distal end of the intestine would just be bile, which would then run through, like water in a pipe, without enough time for intestinal flora to convert Bilirubin to Stercobilin. It would then come out as greenish colored watery stools.