From the Army website. Just follow the advice.
If you are concerned about any child within the UK and feel that they are at immediate risk of harm call the police on 999. If you are worried about a child and feel that they need additional support you should contact your local children’s services or the NSPCC Helpline on 0808 800 5000 or email
help@nspcc.org.uk who will be able to provide advice and support.
If you are concerned about your own child you should speak with your child’s school, nursery, health visitor or GP who will be able to support and signpost you.
You can also talk with your unit welfare officer or call Army Welfare Service Intake and Assessment Team on 01904 882053. Email
RC-AWS-IAT-0mailbox@mod.gov.uk