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.

Sometimes there will be visible sores. If your child develops mouth sores, she may also have throat sores. 

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.