Constipation such as your son's is common in children. Stressful as it may be for both you and your son, this problem usually has no long-term consequences. The most common reason for constipation in young children is "withholding" stool. This may result from stress about potty training, an unwillingness to interrupt playtime or being fearful about having an unpleasant or painful bowel movement. "Withholding" makes stool hard, dry and difficult to pass. Signs that your child is withholding stool include standing on tiptoe and then rocking back on the heels or clenching the muscles of the buttocks.
I discussed your question about safe remedies for constipation in young children with Sandy Newmark, M.D., a California-based pediatrician on the faculty of the Arizona Center for Integrative Medicine. He suggested several approaches to relieving your child's discomfort and improving his bowel problems. First, he suggested a daily dose of 500 mg of fish oil. Make sure the supplement you use provides 250 mg of EPA (eicosapentaenoic acid) and 250 mg of DHA (docosahexaenoic acid).
Dr. Newmark also recommended eliminating dairy foods from your son's diet and trying to increase the amount of water he drinks daily. Although you're already giving your child fresh fruits and vegetables, Dr. Newmark suggested increasing the amounts.
Another recommendation is to give him a fiber supplement such as Metamucil or Citrucel (check with your son's pediatrician for the dose appropriate for his size and weight, and be sure to add extra water for this treatment as well).
In addition to these supplements and dietary changes, you might try to establish regular bowel habits. This means asking your child to sit on the toilet for 10 minutes at the same time every day (after a meal is usually best). Make sure his feet rest on the floor or put a step in front of him.
Andrew Weil, M.D.