Do you know how fast a child is forgetting a language?

I do know that ;-P
I have forgotten German during the eight month at my grandma's home in Turkey. As I came back to Germany, I could only say "Amen" and was forced to speak in sign language. It was not funny not to know what "I want something to drink." in German was, but as fast as I forgot the German as fast as that I learned it again and at the end I spoke two languages fluent...

Another memory from that time is, as I was visiting a few kids from the neighbourhood. This family lived nearby, they had 4 children and I was a single child at that time and loved to spent time with these kids. One day as I was again there, the father of these children said to me (I was 4 years old at that time) whether I know or not that the man I called father, was not my real, biological father... I was so unbelievable shocked, that moment my whole world was destroyed, I started to scream and to shout, to cry. "How can you say that? You are lying, because I know he is my dad, because we have the same feet!" And I stand up and ran home and asked my father, if this is true, if he is really not my real father and he must be my real father, because we have the same kind of feet... My father and my mother were both apalled that an adult can do such things to a child and my father confirmed that he was of course my real father... I will never forget that he has given me, a 4 years old child, peace at that moment!