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If children raise the subject at school staff will be re-assuring them, in an age-appropriate way, that incidents like this are extremely rare and that is is very unlikely that something like this will happen to them, or to anyone they know. To dismiss questions can be counter-productive.
Phrases staff might use are...
"It is very unusual that something like this happens. This is one of the reasons why it is on the news and lots of people are talking about it; it is also because it is very upsetting that something like this could happen. Everyone who has heard the news is very sad and worried.’"
"No-one can completely know why. We know it wasn’t an accident. It’s so, so difficult to understand why anyone would kill other people."
"The police will do all they can to make sure this sort of attack does not happen again. It is really, really unlikely that this will happen to anyone we know"
Staff will talk about people doing 'bad things' rather than there being 'bad people' which can sound very frightening to a young child.
Remember, we are all role models for our children and this includes them learning from the way we react to upsetting events. It's OK if children see us reacting with shock, upset or anger, but they also need to see that we can cope with such upsetting news and rationalise it to our own situation - being calm and re-assuring is key.
You may be aware that schools must actively promote fundamental British Values which are defined as:
Rule of law
Mutual respect & tolerance of different faiths & beliefs
These values are part of our school ethos and are promoted throughout the curriculum and across the whole school. They are frequently referred to in assemblies and at special events. We would actively challenge children, staff or parents who express an opinion contrary to fundamental British Values, including of course, 'extremist' views.
I hope this information is of use,