Thank you for your question. Although without being able to examine you I can not offer you the specific advice on diagnosis and treatment that you need, but I would try to provide you some relevant information about your health concern.
Usually, lipoma remains asymptomatic and occurs due to fat accumulation at the site. Although it hardly changes its shape or grow and rarely causes symptoms but it will be best to get this evaluated with the help of a skin specialist to understand any possibility of other association like nerve compression. Hope this helps.
Obviously you should have a pediatrician have a look at it and determine if it IS INDEED a lipoma. Lipomas generally are not dangerous, unless they cause symptoms or are pushing on a vital part of the body. And if a bump is rather smallish, it can sometimes just be a cyst, which again, a pediatrician should determine just what it is. But you MUST go see a physician about it, because it could be an agressive growth or an indicator of some internal problem that needs to be addressed.