Millions of children have a parent with a mental illness (COPMI). These children are at higher risk of acquiring behavioural, developmental and emotional difficulties. Most children, including COPMI, have low levels of mental health literacy (MHL), meaning they do not have accurate, non-stigmatized information. There is limited knowledge about what kind of MHL content should be delivered to children. The aim of this exploratory study is to identify the knowledge content needed for general population children and COPMI to increase their MHL. A second aim is to explore content for emerging children’s MHL scales. Researchers created and analyzed a literature review database. Thematic analysis yielded five main mental health knowledge themes for children: (1) attaining an overview of mental illness and recovery; (2) reducing mental health stigma; (3) building developmental resiliencies; (4) increasing help-seeking capacities; and (5) identifying risk factors for mental illness. COPMI appeared to need the same kind of MHL knowledge content, but with extra family-contextual content such as dealing with stigma experiences, managing stress, and communicating about parental mental illness. There is a need for MHL programs, validated scales, and research on what works for prevention and early intervention with COPMI children.