It is very important they know sooner rather than later. It is truly traumatic finding out suddenly out of the blue. I was in that exact situation. At 13 yrs old going shopping I was suddenly told in a public place (busy street). Prior to these I suspected being adopted and asked but told I wasn't. I remember the shock and trauma to this day. There are times when I am in public places and panic and feeling disconnected and stressed. Now I am linking that early experience to this. Adopted children deserve to know the truth of who they are.