If the amounts you have 0.5, 0.5, 0.25 refer to portions of a tablet and on MG, then my 2-year old takes the same amount of Cortef as your son.  Gav takes 1/2 tablet (2.5 MG) in the morning, 1/4 tablet (1.25 MG) midday, and 1/2 tablet (2.5 MG) at night.  He is also on a total of 1 1/2 tablets Florinef daily, although I think it will need to be dropped back down to 1 tablet daily at his next appointment.  He did not do as well in linear (height) gain from about 15-18 months, but had made it up again by 24 months.