Dear Doctor, I Found Out On 1st Nov 14 That

Dear Doctor, I found out on 1st nov 14 that my son whose age is only 7 is having a cylindrical power of -3.0 in one eye and the other has -3.25. His mother is also having (-3) power but spherical from the age of 16 onwards. But my son didnot complaint for any vision problem, it was only a routine checkup that we found this problem. Now my question is how long back could he have aquired this problem and what are the chances of this power to increase. how can we keep this in control. do he need to wear glases while studying also ???