Did you actually read what a philosophical zombie is? It is diametrically opposite to what you evidently think this concept is about, since it is not about an entity that "would eventually be affected by some outside force that would change it". And your arguments can't be falsified either ("it [a lonely child] would never develop any sort of sentience that could be measured behaviorally"). That's why I mentioned the concept of a philosophical zombie and said that your own arguments could be used against your point...
That is, you can't falsify if that lonely child is (not) a zombie. You are exposed to the same concept of falsifiability in absolutely the same degree