A 7-year-old boy presents complaining of occasional intermittent lower abdominal pain over the last several weeks associated with a decline in the frequency of bowel movements to one every third day. When he does defecate, stools are hard to pass and sometimes painful. There is no blood in the stools. He has no chronic medical problems, has never had surgery, and takes no medications. Review of systems are negative and physical exam is normal. What is the most appropriate initial intervention for this child?