Thank you, everyone, for your replies. It's good to hear I'm not the only one that finds this behaviour very odd!

As far as my son being in foster care, his maternal grandmother made a false statement to police that Child Protection are choosing to believe, despite my providing them with clear evidence that proves she lied. The fact that so-called "family" refuse to say anything about her abusing me really doesn't help but I'm so used to it- they're more concerned about what will happen to them, despite the statute of limitations having well and truly passed, to do what's right for a child! Government departments here are utterly useless too!

I've spoken to police and they agree that my son's MG's behaviour is very odd and cause for concern but, at this point, there's nothing they can do about it.
My son saw his psychologist this week too but didn't want to talk to her about what's happened, but he knows she's there if he ever does want to talk.

I've also made multiple complaints to Child Protection () which they have continued to ignore for the most part. As far as I am aware they're not investigating but they have made access monitored, which means a worker is with my son and his MG for the first and last 10-15mins of their access, although it took me having a right go at our "worker" for even that to be done! I'm still pushing for completely supervised though as this is not the first time this woman's behaviour has been damaging to my son and I have no doubt there will be more unless she is supervised.

I've been on the phone for most of the morning today and now have the Ombudsman investigating which generally means Child Protection will do what they're supposed to, if for no other reason than they don't want the publicity of subjecting a child to abuse! Child Protection are also required to inform me every step of the way what is happening- they only have the legal right to decide where my son lives and I'm fighting like hell to have even that right removed!

The only possible option left is the possibility of an Intervention Order against the MG and I'm just waiting for a phone call to find out if it is at all possible. If it is I'll be going to the nearest court as soon as possible!

Stressed as hell but getting there. My partner has been great and put up with a lot of ranting from me over the past couple of weeks too!

Thank you everyone for your advice and opinions. It really is appreciated.