Tongue Sores?

My 2.5yr old son has sores on his tongue that come and go, they don’t hurt or bother him at all, they are not contagious in anyway. I had a dentist tell us it’s “graphic tongue” but it doesn’t look that way to me and the sores also change frequently, they go away completely for a week or two and then return and stick around for a month or more. Any insights?