I'm surprised this is news tbh.
Did people think they were given round the clock bodyguards just for prestige?
Or that when security issues (eg perimeter, drive in, selective non-state school so no obligation to admit all-comers) were mentioned at the time of the school being announced and his actual start, that those things were being considered just for fun/exclusivity?
The Royal Family know that they and their children are targets. They have to find a way to live with that.
That there is a threat to Prince George - whether he's at school or anywhere else - is part of his life and always has been.