I think it can sometimes be hard for schools wto walk the line on this. There are some children who use the word in its adult sense. My SIL has been tolf to 'Fuck off you cunt' by a child in infants school. Obviously child is picking that up at home/ deadful etc etc.
Given that some kids may be 'using;' it in innocence and others not, the school may choose a zero tolerance policy. Otherwise you will have parents camplaining 'When X said 'fuck' you didn't to the same to him'
Horrible that schools have to deal with this