You should not introduce milk to your baby until they are at least one year old. Prior to this age, foods like yogurt and cheese may be introduced around six months of age unless your baby has a cow's milk protein allergy.  Yogurt and cheese are more processed than milk, so the proteins are broken down.  Just check the labels to be sure these foods are pasteurized to prevent any food-borne infections.  When choosing yogurt for your baby, be sure to select full-fat varieties.