He is 12 years old and has a white circle on his inner bottom lip it came up last night?

Cancer sore?: Your 12 y old sounds healthy otherwise, if you/he found sudden white spot in his inner lower lip - it could be from pressure ( braces?) bite, irritation by some food,.. likely nothing serious without other symptoms. If spot does not go away see dentist. Try rinse mouth with warm water with pinch of salt. Good oral hygiene is important .