I have become obsessed with citizenship because of this. I thought the biggie was the adoption but, from what I have read with regard to the law, a parent cannot renounce citizenship for a child. Only the person himself can renounce citizenship and they would not except that from a 6 yr. old, however, you do not have to be 18 to renounce your citizenship, you just have to be able to comprehend what you are doing.
That’s pretty much my understanding as well.