Aren't children who move to another country evidence that damage is not as easy to induce as ALG proposes?

Children who are around 9 or younger and move to a different country almost always wind up essentially becoming native speakers of the country they move to. They do typically have a silent period, but is it really true that they don't attempt to speak the language at all? I'm almost sure they would be encouraged by parents and guardians to speak, and would do it at least sometimes, yet they reach native-like fluency. This seems like strong evidence that damage is incurred through a longer-term process of fossilization induced by many repetitions of poor output practices.