A: Being aware of the potential problem is a huge step toward preventing a future problem. Red cheeks alone are of concern and mean they may be reacting to a food, but by themselves they are okay. At four months. I remember my husband kept on saying my son had an allergy because he wouldn't sleep through the night, was very colicky but he didn't have the super red cheeks until he stopped nursing, which seems to be similar timing (after stopping breastfeeding) to your situation. While you are breastfeeding they have your antibodies--and your immune system. After you stop breastfeeding their own immune system kicks in. Also, studies are contradictory. Some have shown that if you wait until 6 months, their chances of allergies are reduced, but others have shown that for kids at risk for celiac, if you introduce grains between 4 and 6 months celiac is reduced. But the study only looked at kids who are at high risk for celiac. Here is an article on this as well as an excerpt:
"According to the results of this study, children who are at increased risk of celiac disease (such as children with a parent who has type 1 diabetes) may be more likely to develop it if gluten-containing foods are introduced prior to or after 4 to 6 months of age. This study also did not look at whether age at introduction of gluten-containing foods increases the risk of celiac disease in infants who aren't at high risk for the condition. But the results of this study haven't affected what health organizations such as the American Academy of Pediatrics (AAP) recommend regarding the feeding of solid foods to infants. The AAP recommends starting an infant on solid foods - beginning with infant cereals, like rice cereal - around 6 months of age. If you have any questions about starting solids or other infant feeding questions, talk to your child's doctor."
If you see them reacting to cereal you could do two things. Either introduce more slowly (1/4 tsp at a time.) Or WAIT to start solids and use homemade applesauce, pears and bananas or vegetable purees.