The Co-SPACE project aims to track children and young people’s mental health throughout the COVID-19 crisis through an online longitudinal survey completed monthly throughout the pandemic by parents/carers of school-aged children aged 4-16 years and young people themselves (if aged 11-16 years). We will specifically track young people from vulnerable groups, such as those from low income households, with pre-existing mental/physical health difficulties, and looked after children. To complement this, and develop a richer understanding of people’s experiences, qualitative interviews will be conducted with parents/carers, young people and people who work with them. Study materials will be shared with international collaborators and data will be linked to explore how patterns associated with youth mental health vary across contexts. The findings will help us identify what protects children and young people from deteriorating mental health over time, what support families need, and how this may vary according to contexts.