My son is 16 months old baby He is on solids and formula milk around 600 ml per day. Solids three times a day. He struggles to poop everyday he is constipated. I give two prunes n one banana everyday. And water around 400ml. Still he passes green hard stools from almost 2 months. Not even once he passed yellow color stools. I tried changing formula and also tried cows milk but tht worsened constipation badly Is it normal for him to pass green stool.