Public Health England's advice on supporting children and young people's mental health and wellbeing during the COVID-19 outbreak:
https://www.gov.uk/government/publications/covid-19-guidance-on-supporting-children-and-young-peoples-mental-health-and-wellbeing/guidance-for-parents-and-carers-on-supporting-children-and-young-peoples-mental-health-and-wellbeing-during-the-coronavirus-covid-19-outbreak. This was published on 29.03.2020 and contains information on how children of different ages may respond to this situation, as well as on children who have learning difficulties and/or autism and whom may already be accessing CAMHS or similar.