I think the unknown child is most likely related to Sera, possibly her mother who was a victim of the black organisations drug from a long time ago (since she is mature and intelligent and reminds me a bit of Haibara <3). Also at the end of one of the episodes she seemed sick because she was coughing. This made me think that maybe after a long period of time from being affected by the apox drug, the victim gets sick and possibly close to death if not cured with a full proof antidote. Sera is so interested in Conan and Haibara because they are as you could say 'fresh' victims. The unknown child also said she doesn't trust Conan yet, so obviously she is waiting to see if he's trustworthy enough to help her and tell him important information she may know about the organization... welp im probably completely wrong but whatever, just thought i might throw out what my theory was. I REALLY WANT TO KNOW THE RELATIONSHIP BETWEEN SERA, SHINICHI, AND RAN
