Around 4 months you can begin introducing cereal mixed with breast milk or formula. After a few weeks you can start introducing pureed fruits and vegetables but only introduce one food at a time in case their are any allergies.
We waited until about 5 months to introduce cereal because we have a history of food allergies, but I think the recommended age is 4-6 months. We started with rice cereal and then moved on to oatmeal. It may take a while for your baby to get used to the whole process of eating (my first took about 2 months to understand how to use his tongue and get it in the bottom of his mouth in order to allow the food to fit in his mouth), so you may not use a lot of cereal for a while. My doctor said we should give a food for at least three days before moving on to a new food to make sure there's no allergy.
We alternated a fruit and vegetable each time we started something new. Once my oldest had moved through all the fruits and veggies, we then moved on to the meats. For our second and third babies were old enough, we skipped the plain meats and did chicken and apples since we knew they were okay with the apples. Save strawberries for the last fruit because they can sometimes cause an allergic reaction (don't worry because I didn't know about that and my kids were just fine).
My biggest advice is to act like any food is the most delicious thing. Your baby will react negatively if you do. Don't get me wrong, baby food is the most bland thing you'll ever taste, but if you make a face, he or she may not even try it.
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