According to the Rambam, the children of the idol worshippers also die by סייף.
This is a biiiiig problem! There is a din that in order to be kosher testimony it must הזמה-ble [עדות שאתה יכול להזימה]. But this is עדות שאי אתה יכול להזימה because of the drasha at the beginning of Makos that we only make them עדים זוממים if the עדות doesn't pertain to their children - לו ולא לזרעו.
עי' מנ"ח תס"ד ועוד ועוד ועוד
