VSM - I didn't give the whole story to my parents and look where that has got me - X2b spun them a huge web of lies - me emotionally and finacially raping him etc.... being a complete victim and I never got a chance to say my piece - you don't want that to happen to you.
At the end of the day marriages fail - 1 in 3 at the last count and going up - if they are living in the dark ages they need to be told that statistic and if I were you I would have no second thoughts about telling them what was happeneing to DS - at the end of the day it would be the best way to get them on your side and may even give them the courage to back you up and help you - it may not but that is a chance you have to take.
You owe him nothing when it comes to loyalty and privacy - you are afterall only telling your parents the truth too - do whatever you can to get support without dragging yourself down to the level where you tell everyone who has ever met you (like my X2b has!!).
If you have to honey show them the social services report and if they still say that you are in the wrong well they don't deserve to be parents to you let alone grandparents to your lovely DS - last night my shrink said to me that I need to let go of my feelings for my parents (well I only have one parent - the stepmonster is not a parent in any guise!!) - I said I don't have any good feelings about them only bad and she said to me that those aren't doing me any good - they are sitting there in my mind slowly rotting - it is true I am so bloody angry with them!!
DP has said that he won't let our children have anything to do with them - which is a relief - I don't intend to even speak to them again - and now I feel a little calmer - he is behind me and to be honest that is all I need.
Sorry for digressing but if your parents can't stand up for you and DS and what has been done to you well IMHO they aren't wortht he worry time and effort - it is almost as hard to let go of a parent as it is a child but to me that parent should have feelings for you that no other human can beat - I am sure no one will feel the amount love I have for my DD, as her mother - and if they don't well that says it all.
Sorry to sound so down about it but you deserve more and so do DS and DD - you have all of us and we will support you in everything that you do - the people who don't well just for a while give yourself time without them in your life - realise how much easier it is to not live with someone's dissappointment - not that they won't feel it still but it is cathartic to think 'Oh fuck off - this has/is happening and I don't give a damn what you think or feel cause it isn't happening to you' - easy to say but hard to do.
I do hope things get better for you and you carry on being strong - you are doing great - I am sooo proud of you still.
I promise we will meet up soon and do something fun - I was in the park on Sunday but didn't see you!!