Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Contact emergency services now if there is immediate danger to the young person or anyone else, a weapon is being used, a serious assault is taking place, a fire has been started, or there has been an overdose.
Move to safety rather than trying to physically control a dangerous situation alone.
Immediate help is also needed for suicidal thoughts with intent, a suicide attempt, severe self-harm, or extreme intoxication.
If a young person reports abuse or exploitation, take the disclosure seriously and contact local safeguarding or emergency services according to the immediate risk.
Seek prompt or same-day professional help if behaviour is rapidly worsening, there are credible threats of serious violence, a young person is carrying a weapon, or there is escalating substance use.
Fire-setting requires urgent assessment even if nobody has been injured.
Arrange a routine appointment if a child or teenager has a continuing pattern of aggression, stealing, property damage, serious lying, school absence, or rule-breaking that is disrupting daily life.
Help is also appropriate when caregivers feel unable to keep boundaries consistent or family life has become dominated by conflict.
Every sign above is quoted from the sofidex article on Conduct disorder. If you are not sure, err upward — it is always reasonable to be checked.