madmondeo,
I've taken a keen interest in this because the lad's welfare is indeed the prime concern here, and thank you very much for the update.
There may be something you can still do - if you feel inclined to? That is, you mentioned that the lad is collected in the afternoon by his grandmother? Well, that's at least a start. You've found out that he is at least being walked back home by a relative. Why not see if the lady would be willing to shed some light on your concerns.
As I said a lot earlier in this post, no decent parent should object to a genuine or reasonable enquiry, and I'd go as far as to say that should apply to grandparents. So, bite the bullet, it would at least put your mind at rest as long as granny's amenable to your approach which would need to be as low key as possible. Go in like a bull in a china shop and you no doubt would get a hostile response.
Try it, I know I definitely would, but as they say "slowly, slowly, catchee monkey"?
Best of luck.