Bonkers!

It does seem OTT if those are all the relevant facts.  

 Those type of sledges can get up some frightening speeds on a steep hill though - it's not like sitting on a £10 plastic job and personally I wouldn't be letting my kids use one on the admittedly pretty long and steep hill they use for sledging.     Bit unlikely the school had a hill like that on their grounds though.  

Even if it was dangerous though I'd have thought a formal warning would have been enough - but as BDB implies we don't know if this was a first offence or not.   

As for schools not allowing "risky" activities now - I'm not so sure.   Primary schools do cycle training on roads now - in my day it was on the playground.   I've been in schools where they practice fencing in PE (secondary admittedly).   My eldest daughter went abseiling and went sailing dinghys with guides before she was in Secondary school.   There probably are examples where H&S is taken too far but not sure it's quite a limiting as is sometimes made out and you do need rules and procedures to protect kids as there are adults (and I've worked with some while working with kids) who adopt a rather fingers crossed approach to safety.   

There are so many instructions issued that come under the "child protection" arena - too many to list individually.

An example, a few years ago, in playtime, a 5yr old girl fell in the playground, cut her knee and needed medical attention.  She was wearing tights and so the tights had to be removed in order to attend to the cut, clean and dress it.  I wasn't allowed to do this on my own (I'm female) - there had to be another (female) adult in the room with me to ensure that I didn't do anything inappropriate.  The quickest and most sensible thing would have been to have sorted it out myself, no fuss and sent the child back into the playground as it was messy rather than serious.  Instead, I had to find another member of staff to be in the same room as me, so while I had to sort that out (whilst not leaving the child alone either - so I couldn't just leave her in the medical room, walk to the staffroom and ask for someone and as it was playtime, most members of staff were not around), the child was growing increasingly distressed.

It took far longer (and IMHO, made the whole situation far worse) to get someone to be in the room with me, but had I not done so, then if the girl had complained to her parents and they had made a complaint to the school, the school would not have been able to defend me as my action would have been in contradiction of the instructions issued by the local council. 

Deadstar wrote (see)

Thought they were called white boards now.