If it's just short sightedness, it could be Pseudo-myopia, in which case don't rush into glasses before looking into it and trying to get them doing more distance visuals and less close up things. At this point it can be a quick fix, unless there is actually something wrong in the eye/s.

https://endmyopia.org/ was where I started and if he still does the 7 day free emails, you shouldn't need more than that to give you an idea of how to help your little one.