This is where the shunning thing really sucks - any mob who'd take out their vendetta against the childrens' parents on the children themselves is a less than moral group. Scum, actually. Perhaps you should complain to your school's administration about the treatment of your kids by another student. Most educational institutions these days have rules against harrassment and try to practice equal opportunity.
It's not even biblical - the Torah does not allow children to partake of punishment for parents' crimes, nor parents for the crimes of children. These are just sick, small-minded people who drag the name of God through the mud for their own sadistic pleasure.