Hello, I work at Primary Children's as an x-ray tech. I perform barium enemas on children every day, and will be glad to explain the process. First off, depending on where you are going for the exam (i personally suggest a children's hospital) there are child life specialists available to help "prep" your son. They are great and explain the exam to him on his level. They often let the kids get involved and play with "doctor" stuff for a few minutes. Once your child feels prepared, the tech will come in and start. The actual tube we use is quite small (he poops bigger than it). It only goes in about 1 inch, and then we use some tape across his bum to hold it in. The Radiologist comes in and starts taking pictures while the barium flows in through the tube. This part is not painful. Most kids say it just feels like they have to poop. The actual test goes quite fast, and the doctors take a number of pictures. You are able to stay in the room the whole time, and the tech and child life specialist are there to help your son feel comfortable and less scared. If he is out of control, some mild restraints (ace wraps) may be wrapped around his legs to keep him from kicking. After the pictures, he can use the bathroom if he is potty trained, otherwise the barium will drain back out into the bag it started in. To be honest, it is one of the fastest exams we do, and sounds way worse than it is. I really suggest getting it, because there are some conditions that can be found that may be contributing to his contstipation, especially something called Hirshprung's. Anyway, I hope this helps. Feel free to call the hospital you schedule at and talk to the techs there, who are always available to answer questions. Good luck!