By the way green stool in babies is almost normal and it might be because of fast movement of the stool in the bowel that it has no enough time to turn brown. Stools
in origin are geen because of the bile secreted
in it but
in the bowel it turns brown. So it might be because he didnt eat enough the past days but be careful that he has no diarrhea. and if this persist u may contact his doctor.