Try wiping it
In a baby, if you see a white coating or white dots on the tongue or inside of the mouth, try to wipe it away (may use a soft baby washcloth).
If the white coating gets better or goes away completely, it is likely not thrush
and may be a coating of milk. If the white coating or dots stay despite scraping, it is likely thrush. Your son's doctor can prescribe an antifungal liquid to treat it.