When your child refuses to eat or drink, has trouble swallowing, or says his mouth hurts or is sore, your child may have mouth sores. You may be able to see red, raw areas or bleeding from the gums, lips or the inside of the mouth and down the throat.

Mouth sores are a common side effect of some of the cancer treatment drugs your child may be receiving. The sores can change your child's usual eating habits and may lead to an infection. The lining of the mouth and digestive system breaks down and ulcers form. This can be very painful. Patients can experience diarrhea.

As the white blood cell count returns to normal, the ulcers heal, and the pain goes away. This can take from a few days to a few weeks, depending on the situation.