Thus far your son is displaying a normal reaction; that is, he is responding in an understandable way to a difficult event in his life. Separation anxiety is the most common resonse in young children to the death (or other type of loss) of a friend. Respond in a patient, supportive manner, and you will likely see the responses wane over the weeks (remember, though, it's still early in the process). If your son's anxiety escalates and expands, and particularly if it interferes with his mastery of the various challenges that are typical for children his age, seek therapy for him. If this becomes necessary, don't wait until a crisis develops, but rather respond in a timely fashion. The gauge to use is whether the emotional reaction is expanding; at this point, the reaction should certainly still be evident, but plateauing.