After ds arrived I decided not to tell people he was adopted unless I really needed to.
This was based on reading on mumsnett adoption threads from some people (whose opinions I respected) that children who joined families through adoption sometimes resented random people (e.g. friends of their parents) knowing they were adopted.
I think the reasoning also went that because adoption nowadays (as opposed to some years ago) often meant children were removed from birth parents because of issues such as drink/drugs/neglects etc. This meant when children said they had joined their family by adoption it could lead to a lot of questions about birth family which children did not always want to answer/or felt they should not have to answer. Perhaps, especially in their childhood and teens, they really wanted to fit in and be like other kids.
Before we met our little boy I was very open with friends and strangers that we were going through the process of adoption. I am pretty gobby, confident and extrovert so I liked talking! And it was talking about me. Now talking about adoption means talking about ds and I am reluctant to do this.
Now I feel I do not want to tell new people we meet about our son's adoption unless it will be beneficial to him, (doctors/teachers etc). I am amazed some people who have known me very casually for a long time had not realised ds was adopted until I told them (I had assumed they would know!).
OK, on to my question. When meeting new people and they ask any questions that could be hard to answer without saying ds had joined our family by adoption, how do you answer them?
What kind of questions are impossible to answer?
I racked my brain and all I could think of was questions about the birth or ds's habits as a baby or perhaps stuff like 'who does he look like in the family?
EG I could honestly say I think ds looks like his mum and mean me or his birth mum, although he does not look very like me! I could even say the same for dad! Both of them! To some extent! I guess I am worried I will be 'caught out' and people will be bothered thinking that I have misled them.
Just looking for ways to avoid or deflect!
Thanks. 
PS - to those who have chosen to tell anyone anything, I am not criticising anyone, just saying how I have chosen to handle things. If and when ds chooses to tell people, it will be his choice but I will still guide him as I feel he cannot un-tell people and he is still only 4.