The truth is, baby's poop changes color all the time, and sometimes it can be a cause of concern for parents, but it doesn't always have to be. Color, in general, has to do with the processing time of food in your baby's system. Yellow stools mean milk is moving through your baby's digestive system too quickly, while green poop means it's taking a bit longer.
Green baby poop can be caused by a number of different things, including breast milk, iron supplements, or when solid foods are introduced around 4-6 months. Tummy bugs can also cause baby poop to be green, and the best way to address those is to keep breastfeeding, since your breast milk is most beneficial for baby's immune system.
If your baby has green poop that's more in the form of diarrhea and less solid, it may be a time to call your pediatrician, as it could be a sign of an infection. Diarrhea in babies and children occurs because the intestines can't absorb enough water from food, often because of a virus. Diarrhea can cause your baby's poop to turn green.
Diarrhea changes the amount of water and electrolytes in poop, and since it's moving more quickly than usual through your baby's system, it can contribute to the color change.
If your baby does get diarrhea, chances are something is irritating them. If you're breastfeeding, maintain your regular schedule, as your breast milk contains plenty of antibodies necessary for baby to fight infection.