Children/ Childhood/ Child	We will use the United Nations Convention on the Rights of the Child (UNCRC) [65] definition of a child: “a child means every human being below the age of 18 years”
Adverse Childhood Experiences	We will use the Centre for Disease Control and Prevention (CDC) (3: p.7) definition of adverse childhood experiences as “potentially traumatic events that occur in childhood (0–17 years)”
ACE: Child Physical Abuse	We will use the term “child physical abuse” to also refer to child physical violence We will use the World Health Organisation’s [87] definition of child physical abuse: “Physical abuse of a child is defined as those acts of commission by a caregiver that cause actual physical harm or have the potential for harm.” The actions inflicted on a child may include: Hitting (with hands or objects), pushing, grabbing, slapping, throwing something at the child, kicking, shaking, burning/ scalding, biting, scratching, breaking bones, drowning, or poisoning
ACE: Child Emotional Abuse	We will use “child emotional abuse” to also describe psychological abuse and verbal abuse Emotional abuse will be defined by the World Health Organisation’s [87] definition of child emotional abuse: “Emotional abuse includes the failure of a caregiver to provide an appropriate and supportive environment and includes acts that have an adverse effect on the emotional health and development of a child.” This may include parents or caregivers: Frequently insulting or criticising the child, humiliation, threatening a child, blaming, and scapegoating, making a child perform degrading acts, not allowing a child to have friends, manipulation of a child, ignoring a child, being absent
ACE: Child Sexual Abuse	We will use the term “child sexual abuse” to also refer to child sexual exploitation, child prostitution, and child sex work We will use the World Health Organisation’s [88] definition of child sexual abuse: “The involvement of a child in sexual activity that he or she does not fully comprehend and is unable to give informed consent to, or for which the child is not developmentally prepared, or else that violate the laws or social taboos of society. Child sexual abuse is evidenced by this activity between a child and an adult or another child who by age or development is in a relationship of responsibility, trust or power, the activity being intended to gratify or satisfy the needs of the other person” Types of sexual abuse can include: Sexual touching by an adult or peer of any part of a child’s body, a child being forced or tricked into touching an adult or peer’s body in a sexual way, an adult or peer attempting oral, anal, or vaginal intercourse, an adult or peer that has oral, anal, or vaginal intercourse with a child Our definition also includes non-contact sexual abuse such as: An adult or peer exposing themselves, an adult or peer showing pornography to a child, an adult or peer making a child masturbate, an adult or peer forcing a child to take/ share/ view child abuse images or videos, an adult or peer taking part in sexual conversations with a child (face to face or online)
ACE: Child Neglect	We will use the term “child neglect” to refer to medical neglect, educational neglect, emotional neglect, and physical neglect We will use the World Health Organisation’s [87] definition of neglect: “Neglect refers to the failure of a parent to provide for the development of the child – where the parent is in a position to do so – in one or more of the following areas: health, education, emotional development, nutrition, shelter and safe living conditions. Neglect is thus distinguished from circumstances of poverty in that neglect can occur only in cases where reasonable resources are available to the family or caregiver.”
ACE: Peer Victimisation	We will use the term “peer victimisation” as an umbrella term to also describe peer violence or bullying Peer victimisation may include: Name calling, other verbal threats and insults, physical assault (hitting, punching, slapping, throwing objects at the victim), and bullying on electronic platforms such as social media, private texts, or emails
ACE: Exposure to Domestic Violence	We will use the term “exposure to domestic violence” to also refer to exposure to domestic abuse or exposure to intimate partner violence between adults in the home We will define exposure to domestic violence as a child witnessing or overhearing domestic violence between two or more adults in their household. Domestic violence is defined using the United Nations’ definition: “Domestic abuse, also called "domestic violence" or "intimate partner violence", can be defined as a pattern of behaviour in any relationship that is used to gain or maintain power and control over an intimate partner.” Domestic abuse between adults that a child may witness or overhear is “physical, sexual, emotional, economic, or psychological actions or threats of actions that influence another person. This includes any behaviours that frighten, intimidate, terrorize, manipulate, hurt, humiliate, blame, injure, or wound someone” [89]
ACE: Parental or caregiver morbidity or mortality	We will use the term “parental/ caregiver mortality” to also refer to parental/caregiver death and will use the term “parental/ caregiver morbidity” to refer to parental/caregiver illness or sickness Mortality refers to the death of a parent/ caregiver prior to a child’s 18th birthday. Parental/ caregiver morbidity refers to “the state of being symptomatic or unhealthy for a disease or condition” [90]. In this case, parental/ caregiver morbidity will not refer to mental illness due to this being a distinct adverse childhood experience category
ACE: Parental or caregiver mental illness	We will use the term “parental or caregiver mental illness” to also refer to parental/caregiver mental sickness, poor mental health, mental disorder, or mental ill-health We will use the following definition of mental illness from Chadda ([91]: p.12): “Mental Illness refers to a chronic disturbance of mood, thought, perception, orientation or memory, which causes significant impairment in a person's behaviour, judgment, and ability to recognize reality or impairs the persons’ ability to meet the demands and activities of daily life.”
ACE: Parental or caregiver substance misuse	We will use the term “parental or caregiver substance misuse” to also refer to injected drug use, heavy alcohol use, heavy drug use, drug misuse, alcohol misuse, problematic drug or alcohol use, substance abuse, heroin, crack cocaine, ecstasy, valium, GHB or cannabis use, prescription drug abuse or misuse We will use the NSPCC’s [92] definition of parental or caregiver substance misuse: “Parental substance misuse’ is the long-term misuse of drugs and/or alcohol by a parent or carer This includes parents and carers who: • consume harmful amounts of alcohol (for example if their drinking is leading to alcohol-related health problems or accidents) • are dependent on alcohol • use drugs regularly and excessively • are dependent on drugs It also includes parents [and carer’s] who are not able to supervise their children appropriately because of their substance use.”
ACE: Parental/ caregiver Separation	We will use the term “parental/ caregiver separation” to refer to parental/ caregiver break-up, breakdown, or divorce We will define parental separation as any relationship breakdown between parents or caregivers with no specificity on marital status or whether the separation was acrimonious or peaceful
ACE: Community Violence	We will use the term “community violence” to also refer to group violence and gang violence We have defined community violence using The National Child Traumatic Stress Network’s [93] definition: “Exposure to intentional acts of interpersonal violence committed in public areas by individuals who are not intimately related to the victim” The acts of violence may include witnessing or involvement in shooting, gang fights, civil wars, stabbing or threatening with a gun
ACE: Collective Violence	We will use the term “collective violence” as a term to also refer to, exposure to state-sanctioned violence, terrorism, rebellions, wars, terrorism, coups, revolutions, rioting We will use the World Health Organisation’s [94] definition of collective violence: “Collective violence includes violent conflicts between nations and groups, state and group terrorism, rape as a weapon of war, the movement of large numbers of people displaced from their homes, and gang warfare.”
Depression	We will use the term “depression” to also define depressive symptoms, major depression, depressive disorders, mood disorder and depressed affect. We will also consider studies to include the outcome “depression” if they measure any symptoms of depression that are specified in the “Depressive Disorders” section of the ICD-11 [95]
Anxiety	We will use the term “anxiety” to also define frequent anxiety, generalised anxiety disorder, obsessive compulsive disorder, panic disorder, social phobia, and social anxiety disorder. We will also consider studies to include the outcome “anxiety” if they measure any symptoms of anxiety that are specified in the “Anxiety or fear-related disorders” section of the ICD-11 [95]
Post-Traumatic Stress Disorder (PTSD)	We will use the term “PTSD” to also define complex PTSD, comorbid PTSD, uncomplicated PTSD, and acute stress disorder. We will also consider studies to include the outcome “PTSD” if they measure any symptoms of PTSD that are specified in the “Post traumatic stress disorder” or “Complex post-traumatic stress disorder” sections of the ICD-11 [95]
Suicidal	We will use the term “suicidal” to also define suicidal thoughts, suicidal ideation, planning suicide, attempting suicide, feeling suicidal, considering suicide, and suicidal tendencies. We will also consider studies to include the outcome “suicidal ideation” if they include measurement of the symptoms or signs of suicidality specified in the “Suicidal behaviour” or “Suicide attempt” sections of the ICD-11 [95]
Self-harm	We will use the term “self-harm” to also define self-injury, self-poisoning, self-punishment, and non-suicidal self-injury. We will also consider studies to include the outcome “self-harm” if they include measurement of the symptoms or signs of self-harm specified in the “Intentional self-harm” or “Non-suicidal self-injury” sections of the ICD-11 [95]
Psychotic-like experiences	We will use the term “psychotic-like experiences” to also refer to psychotic disorders, psychosis, schizotypal traits, schizophrenia, schizoaffective disorder, psychotic symptoms, delusions, hallucinations, magical thinking, persecutory ideas, bizarre experiences, perceptual abnormalities, paranormal beliefs, odd beliefs, paranoia. We will also consider studies to include the outcome “psychotic-like experiences” if they measure any symptoms of psychotic-like experiences that are defined in the “Schizophrenia or other primary psychotic disorders” section of the ICD-11 [95]. The term “psychotic-like” was preferred over “psychosis-like” in line with a large body of literature in which this is the predominant phrasing to describe subthreshold psychotic symptoms in the general population