I was 12 yrs old. I and my parents sleep in the same room. One day I suddenly woke up in the middle of the night and heard my parents doing 'it'. I was frightened. They didn't realise I was awake but I pretended to be asleep ( I sleep on a separate bed in the same room ) . I didn't see them though because there's a curtain between the beds.
Now I think about it, was it a sin to listen to them ( albeit unintentionally ) ?