yeh my DD had taht from birth she is now 16 montsh adn its almost gone. i can feel it occasionally.
hers was the size of a 50cent piece and has just been left alone.
only side effect so far is when she crys her belly button pops out and she doesnt really have an inny or an outy its kinda half half if that makes sense

it doesnt bother her at all, she plays with it and is quite fascinated by it when it pops out.

it really is no problem, unless it starts to eb painfull or so large you can see skin discouloration.