Does Aiden have most of his teeth? Can he chew well? If yes, then I would think that you can offer him any kind of food that strikes his fancy. I have given up trying to offer dd certain foods b/c it is breakfast time or dinner time. Like Tyler, DD been known to eat only broccoli and luncheon meat for breakfast. I think that it really depends on how much to want to go into preparing for meals. I just offer what we are eating and she will eat it if she is hungry enough ( which often turns out to be 5-10 min after she had refused to eat it!
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Don't know if you have Shreddies but dd likes this. It's whole wheat and no sugar added. And the size is perfect for spoon or fingers! I often mix Shreddies, Cheerios, raisins and other dried fruits in little zipped lock bags and placed them in plain sight for dd to retrieve them herself if she is still hungry.
As for the formula, is there a reason why Aiden is still on it? You should check this with your dr if he still needs to be on them. As for milk, I was told that if your lo eats other food items that contains calcium and Vit D, then it is not a big deal if you decides to drop it. Just make sure that he gets enough liquids - ie water, juice, fresh fruits, etc.