Over the past several decades, increasing overweight and obesity in childhood has become a major public health concern. In the UK, as in many other countries, rates of overweight and obesity among children increased substantially in the closing decades of the 20th century (Chinn and Rona, 2001; Lobstein et al, 2003). There were further increases in the early 2000s, up to 2004, but rates of overweight and obesity appear to have stabilised thereafter, even decreasing slightly in recent years (Bradshaw et al, 2016). In England, throughout the 2000s, around three in every ten children aged 2–15 years were classified as being overweight or obese (HSE, 2016). Scotland and Wales report a similar proportion of children aged 2–15 years as being overweight or obese (SHS, 2016; WHS, 2012). A number of other health problems are linked with unhealthy weight among children, including cardiovascular disease and type 2 diabetes, and it can lead to further health problems in later life (Ebbeling et al2002; Han et al, 2010).

As well as their physical health, concern about children's mental health and well-being is now a public health issue (DHSC, 2015). Around one in ten children aged 5–16 years in the UK have some form of recognised mental health problem (Rees and Main, 2016). Relative to the clear upward trend in the prevalence of overweight and obesity among children, and associated health problems, there is more uncertainty around trends in mental health problems among children. As Rees and Main (2016) report, some studies find that there has been little change between 1999 and 2014, but others find that there has been a long-term increase in prevalence of mental health problems among adolescents, both in the UK and in other countries. Data from the most recent Mental Health of Children and Young People, England (MHCYP) shows that the prevalence of children aged 5–15 years with any mental health disorder increased by 1.5 percentage points (from 9.7 per cent in 1999 to 11.2 per cent in 2017). The increase was higher for girls than boys (1.8 vs 1.2 percentage points) and was higher for children aged 11–15 years than for children aged 5–10 years (2.2 vs 1.1 percentage points).