I'm horrified the teacher then took it upon herself without consulting me to discuss this and hold a silence
I totally respect your right not to tell your son about terrorist incidents. I honestly do, and I'm not looking to be nasty or anything here, just presenting a possible situation.
Children in your sons class are talking about the incident in London over the weekend. One of them asks the teacher about it. Teacher does the, 'yes it did happen, you're right' and tries to move on, but those 4 and 5 year olds are pretty persistent and it's clear some of them have something to say or ask about it (lots of young children ask their teachers about current events they've overheard, it's a common occurrence).
Are you suggesting the teacher shuts down that conversation/topic - bear in mind that speaking, listening and questioning are all prime areas of the EYFS - and tells the class they cannot talk about it as she has to consult the parents of every child to see if any need to be removed before they proceed?
That's not realistic. I'm sorry, but it's not. I've been there when children bring up current affairs in a Reception classroom. It's not an indepth discussion of Newsnight, it's a brief chat at an age appropriate level.
I guess I'm just trying to understand what you would have had the school/teacher do in that situation?