The inner wall of our stomach emits enzymes and acids that help digest various foods. Many a time, food contains germs. If there are any germs in the food, acid destroys it. Babies usually produce less acid, so giving them antacids might be counterproductive. In that case, no medicine is allowed without the advice of the doctor.
On the other hand, except for some rare diseases, babies excrete all the necessary enzymes to digest food in the right amount. Moreover, fruits and vegetables all contain enzymes. These enzymes help digest foods. Hence, if you want to use the medicine of enzyme, then you should always consult with your doctor before doing so.
Therefore, if you find your baby is suffering from indigestion and acidity, then it is your primary duty to consult with your doctor before going for any medication.