Infrequent or unusually hard bowel movements -- or difficulty passing them – can affect all children at one time or another. The frequency and consistency of stools vary by age and from child to child, so you just want to watch for signs of strain or deviation from your child’s normal pattern. Common culprits of constipation include changes in diet, heredity or a reaction to potty training. Most cases in children are temporary and, ahem, pass on their own.