There are several reason why your child may only have one kidney:
When a child is born with one normal kidney, he or she should have regular check ups with a specialist doctor, to make sure that the kidney is growing normally
Life with one kidney should not be significantly different to life with two kidneys. Studies have found that people who have only one normal kidney are no more likely to develop kidney failure.
Your child need not restrict his or her activities. However, some doctors believe that children with one kidney should avoid sports, which involve a lot of body contact, like karate.
Your child will not have to restrict his or her diet unless the remaining kidney is not completely normal. In this case, the amount of salt and protein your child eats may need to be decreased. Your doctor will tell you if this is necessary. No other special diets are needed.