Hi
I'm not a legal expert, but I understand CIC's opinion. The child is not your dependent technically until it's adopted. At any time, the real parents of the child could come forth and prove that the child belongs to them through DNA testing. What if they didn't want the child to go to Canada? What if the child then choses to sponsor his/her biological relatives at a later date? And how does CIC know this isn't a case of kidnapping?
This could all become very messy if CIC approved your application. Basically, without adoption, you don't have the right to call the child yours.
And they submitted a false birth registration, whereas if they told the truth, the child could have been included in the application as a defacto family member. Little sympathy.
PMM