After taking moderately high doses of Prednisolone for 6 years to treat Polymyalgia Rheumatica, I have recently been diagnosed with steroid-induced Addison's Disease/adrenal insufficiency.
The diagnosis was long and arduous and it was a relief when an answer was found.
My understanding of the condition is that it can successfully be treated with a proper amount of replacement cortico-steroid.
At present I am still seeing an endocrinologist to try to determine the"proper amount".
This involves measurement of any existing cortisol and aldosterone levels in my body, and adjustment of replacement steroids to suit.
I would think that the process of "balance" of any existing residual hormone in the child's body and the administration of artificial steroid hormone would be similar.
I have been told that with correct treatment, I can lead a normal active life. I have no reason to doubt this advice, and I am sure the same would apply to a child.
I hope all is well with your 7 year old.
You asked for advice, so I am going to stick my neck out and offer a small piece.
Your 7 year old is possibly worrying a lot about the diagnsosis without expressing the worry. If this were my child, I would seek out some psychological help for him/her in dealing - not so much with the condition - but with the obvious worry of the adults in the family.
Best wishes.