I doubt he even notices his last log in. I'd log in if you can...who cares? He's a minor by law and you can do what you want in that regard...if you think he's in danger, do it.
That aside, I obviously do not know the entire story, but if you're that fearful of his interest in his choice of religions, it can't possibly be something as benign as Wicca. Is it satanic worship? Because, if so, that's not Wiccan and anyone who tells you it is, doesn't know what he/she is talking about. Wicca has nothing to do with satanic worship in any way whatsoever and it's more than a little disconcerting that you or anyone else thinks it is.
Signing on and doing as Janna said, "hide on line now" under account settings sounds like the best way to go.
