My son has several stomach aches off and on

Just be happy that they found it! My son was 2 when they found out his left kidney (severely scarred- only 20% functionality in that kidney) and right kidney working like a charm (size of 7 year old).  Left kidney started off little; didn't grow because of reflux during pregnancy. I had a crappy OBGYN that didn't find it. Would have been fixed in womb or at time of birth but no such luck that time :(

IF that is what you hear (one good kidney); that is a good thing. One kidney helping to take over the other is the best situation when involved with having to face a kidney is smaller than the other. My son had Kidney reflux surgery at 2 and 1/2. Successful and he is doing pretty well so far. Luckily his kidney was functioning right at 20%. Cut off is 15% here. Then they usually remove it.   It is something usually heretical.. I had a reflux surgery when I was four but for a different part of the urinary system.  Likely this was something he developed at the time of birth. I know I know.. it was something I hated to hear.. There was nothing I could have done to make that different during pregnancy. It was my genes that caused the birth defect.

He should be and live normally amongst others with little or no problems.  Just be pro-active in his urinary / bowel care and dont let him get hit in the smaller kidney area as much as you can. This could create problems.  But remember!! Many many people can live perfectly fine with 1 kidney and do sports etc. My aunt is one of those. She donated her kidney to save her sister who was dying of diabetes.  I was worried and can say I still am; but I will watch and be overall protective of his health because of this..

I wish you luck!! No matter what happens your son is going to be fine!!