How Will I Know If One Swollen Node Is Due

How will I know if one swollen node is due to cancer ? I have one behind my ear and it's been there for over 6 months . It doesn't grow , it's not too moveable but it's tiny and squishy .
My 3 year old has had one on his neck for the same amount of time and it rolls under my finger , very moveable and it's less then 1cm . It's giving me anxiety . He just had an ultrasound and everything came back normal , and I'm currently waiting for mine . And none of us have had any infections or any flu , there's nothing visible that we can relate to the swollen nodes . Please get back to me ! Thank you !