Of course not, that would be horrific. BUT, if they truly believed their religion it really shouldn’t be horrific but lucky. If after 8 years old you are fit to be judged by your Heavenly Father, but before that day you’d have a free pass to the best heaven, logic would dictate that mass-murder of these kids was actually a very good thing to happen. Sure, you’d suffer here on Earth because of humanly feelings of sadness and anger, but that is pretty meaningless in the span of your whole existence.