My son was oversuppressed for about 4 months when he was about 12-16months old.  He literally did not grow at all.  If your child is putting on a lot of weight and is beginning to look "cushoid" meaning they have the really chubby cheeks, I would get the levels checked since it sounds like your child could be oversuppressed.  My sons doses are extremely low.  He is still on the cortef suspension and he takes .5 mg in the morning and afternoon and .25 mg in the evening.   He is also on a 1/2 tablet of florinef once daily.  Hope this helps.