I have just looked at what safeguarding legislation and guidance is used in Wales. The NSPCC have these useful guides:
learning.nspcc.org.uk/child-protection-system/wales/
and even more relevant this one:
learning.nspcc.org.uk/research-resources/schools/safeguarding-legislation/
This would appear to be the appropriate legislation:
gov.wales/sites/default/files/publications/2018-11/keeping-learners-safe-the-role-of-local-authorities-governing-bodies-and-proprietors-of-independent-schools-under-the-education-act-2002.pdf
Chapter 3 seems to be the most relevant to the issue of confidentiality that you highlighted. Just looking through it, the points that seem most applicable are:
3.16 not promise to keep what they have been told secret or confidential, as they have a responsibility to disclose information to those who need to know: reporting concerns is not a betrayal of trust.
report their concerns to their line manager or (if appropriate) the member of staff in their organisation with designated responsibility for child protection.
3.33 Many professionals are under a duty of confidentiality. This is important in maintaining confidence and participation in services and thereby helping to protect children’s health and well-being. But, as relevant guidelines make clear, the duty of confidentiality is not absolute and may be breached where this is in the best interests of the child and in the wider public interest. If professionals judge that disclosure is necessary to protect the child or other children from a risk of serious harm, confidentiality may be breached.
3.37 Professionals should discuss any concerns about a child’s welfare with the family and, where possible, seek their agreement to making referrals to social services. However, this should only be done where it will not place a child at increased risk. The child’s views should also be considered in deciding whether to inform the family in some circumstances, particularly where the child is sufficiently mature to make informed judgements about the issues.
There are some other links contained within the document which might be worth checking out.
This article by Sarah Phillimore, a barrister, is also quite interesting as explains how similar guidance is failing to understand the interplay between the Gillick Competency of a child and the importance of parental responsibility. The section on the importance of parental responsibility which is recognised and protected by domestic and international law may be especially relevant because "in 2011 the Rights of Children and Young Persons (Wales) Measure made Wales the first, and so far only, country in the UK to make the United Nations Convention on the Rights of the Child (Office of the United Nations High Commissioner for Human Rights, 1989) part of its domestic law. This ensures that children’s rights are included in all policy making in Wales."
Anyway I don't know if that is of any help or relevance. I am no LangCleg or R0wantrees.