This thread is making my head hurt.
We do not encourage children to keep secrets with adults. You can wrap that up whatever way you want, but it doesn't change it. No NEU guidance, or school 'policy' can override that.
Safeguarding is like a very messy jigsaw puzzle. When undertaking enquiries, the Social Worker has to painstakingly work through all the information, gathering different threads to build the bigger picture. Any serious case review (in either adults or children), without fail, indicates issues with communication between involved people, and usually it is a failure of communication between different agencies. When we start to work within a culture whereby it's acceptable to not disclose x or y, for z reason, mistakes happen. Often when I'm interviewing other professionals, they have no idea that certain things they've said have extreme relevance to the case, and this is why we work to a 'no secrets' policy (quite literally in adults).
A school teacher, cannot, and should not, be making decisions and final judgments about what families should and should not know on the basis of the 'maybes' and 'what if scenarios' being talked about in some posts. That is not within their statutory remit. Being a teacher does not override a parents' parental responsibility. We know that people, in general, are very poor at assessing risk, and this is amplified when the risk assessment is being undertaken by an individual without outside input. That is why safeguarding investigations are not completed by one individual alone, and why Social Workers are specifically trained in the way we are. I am alarmed by some of the statements made by PPs which suggest that they take an autonomous approach towards safeguarding, and in some cases they appear to be doing their own version of a safeguarding investigation (& badly at that). That is not your role and you are not trained to do so. As I said before, you should not be stepping outside your role and area of expertise. If you identify a safeguarding issue, you refer it, you do not attempt to investigate it yourself and come to your own conclusions.
If you don't take anything else away from what I've said, please remember that abuse thrives on silence and by being silent, you have no idea what you are being complicit with.