That is awful maxgran - how old is he?
They are not supposed to have Facebook pages until they are... I think it is 13. But many are allowed to. Big pressure to be one of the crowd.
If these are school friends sending him these, then the school can quite justifiably get involved. They should have an ICT use policy and lessons on the subject - teaching children to stay safe online and to highlight that online bullying is not acceptable, whether it happens in school hours or not.
This is a kind of intimidation and should be banned or discouraged. Unless young teens are told not to do it, they will think it is fine.
Most workplace policies expressly forbid them.
So my recommendation is for this parents to speak the school about this.