My son is only five years old and has a canker sore. what can i do to ease the pain and prevent this from happening again?

Canker sore: There is no one common cause for canker sores (aphthous ulcers). Some result from virus infections, some from trauma (biting the lip, tongue or cheek), some from stress (usually in adults). The ulcers will heal by themselves in 7-10 days. Avoid spicy foods and further trauma to the sore. Get orabase ointment otc, which is an oral bandage, and apply to the ulcer before meals.

Sore: First treat the symptoms with topical anesthetics/motrin ask your dentist. Second they will come back at some point as the virus that causes them lives in the nerve ganglion. Reassure him and treat the symptoms.