You're picking up your son's energy. I've had similar experiences with objects owned by other people. I have a healer friend - her crystals carry a very strong healing energy. It comes from her, not the stones themselves. They just carry it.
Like others, I'd strongly suspect you're feeling your son's energy. Perhaps he gravitates to it when he's feeling particularly peaceful? I would also suspect it's a form of psychometry. It's interesting to me as I've wondered whether I could develop any skills in psychometry and it hadn't occurred to me the obvious place to start is with objects of people close to me, or at least people I know. Hmm, it also occurs to me I should lose a couple of objects from someone in my house