The best indicator of the severity of the diarrhea is its frequency. A green stool also points to very rapid passage and moderate to severe diarrhea. The main complication of diarrhea is dehydration from excessive loss of body fluids. It's dehydration you need to worry about, not the presence of diarrhea. Occasionally it is caused by bacteria or parasites.
Diarrhea can be due to excessive fruit juice or to a food allergy.
If only one or two loose stools are passed, the cause was probably something unusual your child ate. Expected Course Diarrhea usually lasts from several days to a week, regardless of the treatment. The main goal of therapy is to prevent dehydration by giving enough oral fluids to keep up with the fluids lost in the diarrhea. Don't expect a quick return to solid stools. Since one loose stool can mean nothing, don't start dietary changes until there have been at least two.