Hi Jenny,
I am Jemmm's wife. Good to meet you (albeit online!).
Firstly, everyone with a 'child in need' (as set out in the Children Act '89 - and it can be useful to quote these things) has a right to a full children's social care assessment. (i.e. as you say, core assessement). Further, under the Carers & Disabled Children Act (2000)you have a right to request an assesment of your needs (as distinct from those of your son, (for example, respite, support etc.)This is really important but lots of social services authorities are not very good at it - and many forget to tell you about things - we've experienced this too.
If this is not happening, as you suggest, I think you should make a complaint. This tends to get things moving (I spent 15 years as an inner London complaints manager for a social services department). If you make a complaint, put it in writing to the 'children's social care complaints manager' (it's a statutory role) with a cc to to the director of children's social care (or equivilent), the lead elected member for children's social care in your authority area and your local MP. If I were you I would also give a covering note to your MP asking him / her to help your cause and monitor / intervene in your situation. If you need some help finding out who all these people are, let me know - I will happliy let you know. and I'll also help with the drafting of the complaint if that's in any way helpful.
I know it can feel very uncomfortable making a complaint, but it does often move things along and also show that you are serious. Certainly, my experience is that lots of people with children with a disabilty need to make complaints to move the system. The complaints process is also statutory, set out in the Children Act (1989)and provides parents with a three stage process, whereby you can ask for an independent investigation if you are unhappy with the first response, and if that doesn't work, a Review Panel like an informal court room experience with independent people reviewing the situation and making recommendations.
I do hope this in some way helpful. I do know how hard this is - we are at a similar stage. Let me know if you need some help negotiating the system,
Best wishes,
Emma