Adoption conversations always happen in the car for us (and many of my friends). They feel safe there. They know you can't sit eye to eye with them and answer. They also have your attention.
Tinkerbell is 7 now and asked about her birth dad the first time when she was about 4 1/2. We only know a limited amount of details about him. And she only asks about him a few times a year. When she does we remind her of what we know and it's enough for the time.
The most recent conversation, as always I answered the best I could, but we were both left with some unanswered questions. I have a feeling she would really like to see a connection to her skin color in someone so we talked about the fact that they share that in common. I asked her if a picture might help her and have been able to get one so we will be sharing that with her soon.
Having pictures of her biological family available to her (and Flower) to see when she wants is important to us. Both our girls have pictures of them with their bio mom in their rooms.