I just found this and thought it fairly reassuring, I hope you do too:
When are further tests advised?
Tests are advised in some cases to check on the kidneys and/or bladder. As a general rule, children under the age of five years who have a first urine infection will usually be referred to a kidney specialist with a view to having some tests. Children over the age of five who have two infections within the space of 12 months will usually be referred to a kidney specialist with a view to having some tests.
The tests that are advised may vary depending on local policies and the child's age. They usually include a kidney scan. There are various other tests that can check on the structure and function of the urinary tract (the kidneys, ureters, bladder and urethra). If a child is referred to a specialist for tests, your doctor may prescribe a daily low dose of antibiotic whilst waiting to be seen. The aim of this is to prevent a further urine infection until the results of any tests are known.
The results of the tests are normal in most cases.
In some cases, a problem is found. The most common condition is called 'vesico-ureteric reflux'. This is a problem at the junction where the ureter enters the bladder. In this condition, urine is passed back (refluxes) up the ureter from the bladder from time to time. This should not happen, as once urine gets to the bladder it should only pass out of the urethra when going to the toilet. This condition makes urine infections more likely. Also, infected urine that refluxes from the bladder back up to the kidneys can cause kidney infection, scarring, and damage. In some cases this leads to severe kidney damage if urine infections recur frequently. Other rare problems that may be found include kidney stones, or congenital abnormalities of parts of the urinary tract.
Diagnosing urinary tract problems in children can make a big difference. Treatment may prevent kidney damage which might have caused high blood pressure or kidney failure later in life.