I'm going to assume that the author might but nowhere in the past has there ever been magical birds and angels and magic and a kid running an entire large company that's been reincarnated. So having children executed is solely based on the author's creativity to me. Is it because the author doesn't know what to do with the little sister? That's just lazy writing then.
More than just a kid changing they explain it as her soul is absolutely white in that case it is bad as it indicates that she cannot change(I assume) as souls I would take it do not change it also links to why she is so evil she does not have the ability to comprehend good and bad right and wrong that's why they judged she cannot change (also the angel thing)
So... What the heck was this trial ? It was like : "They did it !" - The End.
I'm gonna assume the gladelises being the plaintiffs and the duke the defendant is a bad translation mistake, but that aside, the duke just accused them, Karshian gave testimony and that's all. That's the whole freaking trial. Like... What ?