Charlie Brown may be the most famous young sufferer of undiagnosed chronic pain -- his constant complaints of stomachaches when something went wrong could have indicated a more serious problem.
While the lovable Peanuts character is fictional, pain in children is very real. The American Pain Society found that 15 percent to 20 percent of children are affected by chronic pain. Experts say, though, that many kids suffer because the cause of their pain is left undiagnosed.
There are about 30 clinics across the United States that focus on pediatric pain, leaving much of the country with no specialized treatment available.
A child's pain may be ignored because they may not be able to communicate adequately. Or parents and teachers may think they are seeking attention. Some children even see their pain as punishment for doing something wrong and are scared to complain.
Whatever the excuse, children feel pain too, even if it cannot be pinpointed to a specific problem.
"Pain is what a person says it is," said Kenneth R. Goldschneider, director of pain management at the Cincinnati Children's Hospital Medical Center. "If a child says they are hurting, there is no one on the planet who can say otherwise. The question is what's driving the pain, where it comes from and how intense it is."
Experts in pediatric pain say the biggest difference between assessing and treating pain in children and adults is the child's difficulty in communicating what they are suffering from and how much it hurts.
"With adults you just ask them, assuming they have the ability to communicate," explained Goldschneider.
A doctor may use different scales of assessment depending on the developmental stages of a child, said Michael Joseph, associate director of the Comfort and Pain Management Program at Children's Hospital Los Angeles.
Infants, for example, tend to react in particular ways when suffering from real pain, according to Joseph. They will furrow their brow and shut their eyes tightly while crying. The corners of their mouth could be pulled up tightly, their tongue cupped while crying and they could cry in a slightly higher pitch.
"We must observe because we can't actually ask them," Joseph said.
Toddlers and children may be able to say that they hurt, but may not be able to explain the intensity of their pain. Goldschneider stressed that how you ask a child about pain is important.
"Asking a 5-year-old, 'Do you hurt?' you may get a completely different answer than if you ask 'You hurt, don't you?' " Goldschneider explained.
For children aged about 3 and up, Joseph uses what he called a "faces system" of assessing the intensity of their pain. The child is presented with photos of five to 10 children showing different levels of distress in their facial expressions and asked to point to which one most closely resembles what they feel, he said.
A child may go through a number of doctors and a number of tests, and the diagnosis may be that there's nothing wrong with them.
The experts explain that if a child is complaining of a stomachache and every test shows there is nothing wrong with the stomach, that does not mean that something is not wrong.