That's my husband's response too. Normally I am a go with flow kinda girl, except when it comes to the kids.
I had Boy 1 prior to my husband and I dating, and my husband adopted him when he was 3. We have been very open with the kids about the adoption. I spent years going over the eventual conversation with him about who is father is and why he wasn't around. I had this very eloquent talk planned and everything. One day my son asked the long anticipated question, "Who is my biological father?" I told him his name, and he asked if had met him and I said no. I explained he wasn't prepared to be what Boy 1 needed and that he trusted me to be a good mother and to give him all he would need. He said "oh," and that was that. It took all of two minutes. Very anticlimactic. Maybe I should take my cue from that.