You should start an assessment if you have tried to meet the child or young person’s needs from within the full range of universal provision, without progress or success.
You now need to get additional support from other services. You need to decide whether the needs identified can be met by involving one other service, or if multiple services may be required. Discuss your concerns with the family (and young person as appropriate). You need their consent to share information with another agency to get additional support.
If you decide the child or young person’s need can be met from one other service and you have consent, you can refer to the service directly.
If you decide their needs require support from more than one service and you have consent, you will need to start an early help assessment with the family. You should check if there is a plan already in progress.
See also the working together to safeguard children guidance on assessing need and providing help, on the GOV.UK website.