Thanks for posting your query at HealthCareMagic. I have carefully gone through the details provided by you. In normal scenario, the food passes down our gastro intestinal tract and reaches the anus. By the time it reaches the anus, the digestion and absorption of food principles are complete. If the movement of the bowels is improper, two different problems will result. Firstly, the food digestion and absorption would get affected as revealed by poor weight gain in the case of your son. Secondly, if the forward movement is inadequate, the food along with the digestive juices like the acid in stomach will flow backward as demonstrated by the acid reflux and vomiting of your child. So all that needs to be done in case of your child is regularising the bowel movements. The question is how. I would make a few suggestions. 1. Remove milk and lactose based foods altogether from his diet. Yogurt/curd can be continued. 2. Remove wheat based and gluten containing foods altogether from his diet 3. Include much of fibre rich food items like green leafy vegetables. You may mash them with the boiled rice based food containing pulses. You may include isabgol husk. 4. Otherwise make his food just the mashed up version of adult food slightly low on spices and chilly. My suggestions remain valid with the consideration that he might be having malabsorption syndromes or coeliac disease. You need not be concerned about them at the moment. I hope that should relieve your problems. You can revert back directly to me in case of further queries by clicking the link on my name.