Early days in assesment

I posted a few weeks back regarding the issues my son has and over the last week he has begun the journey to diagnosis. We are getting some conflicting views from the Dr and Hv - the hv says because he is affectionate and spoke to her at the meeting it isnt autism but probably a behavoural issue that needs addressing. My Dr agreed that he could be very intelligent and manipulative with anxiety issues but did display some autistic symptoms. I had always felt they should be looking at mild aspergers and OCD but I guess we wont know until he is assessed. 

I have a couple questions which I hope you can help with. I totally understand that the initial referal appointment can take some time is there an average wait time? Also the Dr mentioned that the whole family would most likely need to be present for some of his assessment which includes my 7yr old daughter. I am wondering what would be the best way to explain this to her? I dont want her worrying and its hard to explain to adults what my son 'might' have let alone a child. 

Any advice is always appreciated. x