Yesterday I went to the hospital with my 63 year old mother, who was receiving her results from a recent CT scan and we discovered that she had been born with one kidney (the scan was unrelated to ker kidneys). Apparently the other kidney has grown larger to compensate over the years. She has lived a full and active life without knowing this (she eats and drinks what she wants, used to smoke, had 4 children, worked until retirement, had surgery), and suffered no ill effects at all.
I hope that this helps,
Best wishes to your family,
Tamsin

Our son was also born with one kidney. We found this out prior to birth with a prenatal ultrasound. After giving birth to our son, the doctor had our son undergo some testing to make sure that his one kidney was stable then referred us to a nephrologist. We went for a year and had tests done to monitor his kidney function. We found out that his left kidney grew in size to make up for the missing right kidney. During our visits with the nephrologist he informed my husband and I that we should allow our son to be in contact sports but buy protective equipment to protect the kidney that he does have. The nephrologist also informed us that he has seen more kidney damages from people playing golf then any other sport due to the constent twisting that is required in golf. Also diabetes runs on both sides of our families so we have to watch for diabetes.  So before we got a clean bill of health from our nephrologist we were told to make sure that any urology related issues needs to be addressed seriously such as kidney pain on the side of solitary kidney, lower abdominal pain, strong odor of urine, burning when the child urinates, not urinating for long periods of time (such as not urinating for 4 + hours), fevers with any of the previously mentioned symptoms, or signs of blood in the urine.
When our son was about 2.5 years old he went 16 hours without urinating. Of course we both freaked out and took our soon to a local hospital in the new area that we recently moved to. The ER straight catheterized our son to collect a sample to test for infection. Came back with the Dx of a stomach flu. (I am a medical assistant so keep in mind I know the difference between a flu and something wrong with the urinary tract). We brought our soon home and he would cry and double over whenever he felt the need to urinate once the pain went away he would vomit. So I called the doctor that our son previously went to prior to our move. He instructed us to take our son back to the ER. I informed him of what they had told us and that I did not feel comforable sending our son there so he recommended us taking him to the next town over which is about an hour away from where we lived. So off we went. Once again they were unable to get our son to urinate so they straight catheterized him again and set us up with an appointment the next morning with a local doctor. So again we went home and I monitored our son throughout the night and still did not urinate on his own. When we arrived at the appointment it had been 10 hours since the catheter in the ER and still no normal urination. The doctor's office again catheterized our son but this time did not send us home but start over to the hospital were he was admited. There he underwent several tests and catheterized one more time. Poor guy he was catheterized 4 times within a 24 hour period. So a local Urologist came in and evaluated our son and informed us that he was having bladder spasms and that this is normal for some kids when they are in the process of potty training. We were finally informed of what was truely going on and given medication to help relieve the spasms. We stayed in the hospital until our son was able to urinate on his own then sent home. Since then we havent had an issue with him holding his urine.
I now work for a well known Urologist in the same town that the ER told us that it was just a stomach flu. I am able to relax a little more knowing that if anything goes on with our son my boss can take care of him.
So my advise to any parent that has a child with one kidney, allow your child to live a normal life but always keep a close eye out for the little signs that most parents would over look. Increase fluids, stay away from sugars, monitor urination, and provide protection equipment when needed and your child can live a normal and safe life.
I hope our story can give comfort to another family that maybe having the same kind of issues. There is hope just stand up and be a good advocate for your child.