DS, 2.5 has a small, round lump under the skin (e.g. not visible)at the base of his neck, where his shoulders meet. It's very round, about the size of a ball on a tongue stud or belly bar/ ball bearing, maybe a bit smaller. Causes no pain and is not visible on the surface, but you feel it when rubbing suncream in. My mum noticed it first and now nursery have mentioned it (so definitely odd and not bone etc). It hasn't grown.