Solid foods, in and of themselves, are not the problem. How hard or how soft stools are depends mostly on how quickly things move through the colon. As stool travels along, water is absorbed out of it, so the stool gets firmer and dryer. (Diarrhea stools are loose because they go through fast -- they don't go through fast because they are loose!)
Whenever there is a major change in diet, there can be a change in stools as the body adjusts. Some kids are more sensitive to changes than others. Sometimes just increasing the fluids will make a difference. Water and apple juice are great choices, and prune juice is even a bit more powerful.
Fruits and vegetables are great for him too -- especially peas, pears, peaches, plums, and apricots. Things made with white flour and white rice will often make stools harder, but whole grains help (they help either diarrhea or constipation -- they tend to bring stools to a middle consistency if the kids get enough fluids).
Some kids needs a stool softener. Maltsupex is one of the gentlest, but it is very expensive. Unprocessed bran -- half a teaspoon once or twice a day -- is about as effective and much cheaper. Again, make sure your child is drinking plenty. Bran without fluids would be a brick.
The information on this Web site is designed for educational purposes only. It is not intended to be a substitute for informed medical advice or care. You should not use this information to diagnose or treat any health problems or illnesses without consulting your pediatrician or family doctor. Please consult a doctor with any questions or concerns you might have regarding your or your child's condition.