Hello, Welcome to Health Care Magic. I read carefully your query and I understand your concern. You do not have to worry about, as long as your child is acting normally and drinking and eating enough. The condition you are describing is benign. Normally, the brown color of the stool is made by a substance called bilirubin. When stool passes through the intestines rapidly as is your sons case, diarrhea, there may be little time for bilirubin to undergo its usual chemical changes. Thus, stool can appear green in appearance due to rapid transit. Mild diarrhea usually passes within a few days and kids recover completely with care at home, rest, and plenty of fluids. Hope I have answered your question, if you have doubt then I will be happy to answer. Thanks for using health care magic. Wish you and your son a very good health.