A white dot or dots on the cornea
generally means an infiltrate or infection. There are many sources but, in a child it often is secondary to a common cold
. These are most often viral. His vision is probably fine because it does not involve the center of the cornea. Does he experience glare on looking at light or sunlight and is there some watering? Since he is a child and since it does involve the cornea I recommend you have him examined by an ophthalmologist earlier rather than wait.