There are several conditions that can affect knees during childhood and adolescence, most commonly it is nothing to worry about but occasionally it can be the result of a condition that requires immediate Orthopaedic intervention.
If you are concerned about knee pain, you should make an appointment with your GP in the first instance and they will be able to ensure you are appropriately screened.
If you would like a more in depth understanding of the anatomy of the spine, check out – AnatomyZone – Your Guide to Human Anatomy and search ‘knee’.