I completely believe that being hungry affects behavior and even the types of food fed...BUT this child is 4yrs old. He is walking around smacking people. That is poor behavior and the parent is making up excuses. Parents that jump to blaming everything else (including chocolate chip pancakes) are typically the parents that never address the situation and just shrug it off. I'd be more likely to term this child due to the parents response to your addressing concerns about his behavior. Had the parent been open and willing to help address the behavior I'd be tempted to keep him on and work with them to get him sorted out.