If the barium study has been reported as normal, then your child has constitutional constipation. This starts with poor eating habits and poor toilet training. Once the stools become hard they cause pain, cracks the anal skin resulting in fissures. This further aggravates the constipation. Most importantly, the stools must be softened using mild laxatives. Simultaneously, improve the diet to include lots of fibre. Local application of creams to the anus before passing stools will make the act more comfortable.