The Gemara or Tosfos (don’t remember which) ask why we don’t do an autopsy on all murder victims to check if they’re a Treifah even if that could get the accused acquitted because it’s not worth Nibul HaMeis.
That seems to be comparable here. Maybe protecting society from a potential child murderer is more important? I don’t know. We would need to see the Noda Bihudah in-depth. I haven’t looked at it in a very long time.