This school has decided that, to prevent injuries from being hit with (possibly contaminated with grit or rocks) snowballs, children are not allowed to touch THE SNOW.
https://www.theweathernetwork.com/news/articles/school-children-banned-from-touching-snow-in-london-uk/96607/ (https://www.theweathernetwork.com/news/articles/school-children-banned-from-touching-snow-in-london-uk/96607/)
If they've managed to write this as incompetently as most school administrators write rules, they've managed to ban children from being outdoors on the school site while it is snowing and from being on any surface from which snow has not been removed.
As the article notes, MOST schools would just ban throwing snowballs.
I do hope some children exploit this to say they are banned, BY THE SCHOOL, from actually going to the school if it is snowing.