My thing is, the tadpoles have teeth. The process isn't purely magical or metaphysical. They still bite and eat and that's likely to go as well for them as a human trying to bite and eat a warforged.
A good chunk of a warforged is actually living wood, not metal, unlike Autognomes, which are almost entirely metal or none living materials, which is my Fanon reason why Warforged are concidered humaniods and Autognomes are concidered contructs.
So yeah a Tadpole could chew through the wooden parts like a termite.
