Re: 5 year old has kidney infection

 My friend's daughter has a kidney infection. She is 5 years old. Is this a common a thing?

Generally no, but this is likely a bladder infection that got up in to the kidneys.  This can occur if she got dehydrated or got E. coli from feces in to the urinary tract from improper wiping.

What is recommended for someone this young with an infection?

Pure cranberry juice or blueberry juice should work.  Not something like cranberry juice cocktail.  Some health food stores will sell pure cranberry or blueberry juice or their concentrates that can be diluted down and sweetened with something like stevia.  These would be easier to get down a 5 year old than uva ursi, which is normally my first choice.  She should also drink plenty of water and urinate frequently to help flush out the bacteria.