Children and young people are likely to experience high rates of depression and anxiety long after the lockdown ends, according to a review.

The research draws on more than 60 pre-existing, peer-reviewed studies into topics spanning isolation, loneliness and mental health for young people aged between four and 21.

It concludes that young people who are lonely might be as much as three times more likely to develop depression in the future, and that the impact of loneliness and mental health could last for at least nine years.

Authors of the study, published in the Journal of the American Academy of Child and Adolescent Psychiatry, said clinical services need to be prepared for a future spike in demand.

The study comes as NHS England’s top doctor for children and young people’s mental health has urged parents to be alert to signs of anxiety, distress or low mood as some pupils return to school on Monday.

Dr Maria Loades, clinical psychologist from the Department of Psychology at the University of Bath, said: “From our analysis, it is clear there are strong associations between loneliness and depression in young people, both in the immediate and the longer term.

“We know this effect can sometimes be lagged, meaning it can take up to 10 years to really understand the scale of the mental health impact the Covid-19 crisis has created.

“There is evidence that it’s the duration of loneliness as opposed to the intensity which seems to have the biggest impact on depression rates in young people.

“This means that returning to some degree of normality as soon as possible is of course important.

“However, how this process is managed matters when it comes to shaping young people’s feelings and experiences about this period.

“For our youngest and their return to school from this week, we need to prioritise the importance of play in helping them to reconnect with friends and adjust following this intense period of isolation.”

Members of the review team were also involved in a recent open letter to Education Secretary Gavin Williamson.

They suggest that the easing of the lockdown should be done in a way that provides children with time and opportunity to play with peers.

Schools should be resourced and given clear guidelines on how to support children’s emotional wellbeing during the transition period as schools reopen, the experts say.

They call for play – rather than academic progress – to be the priority during this time.

Their letter concludes: “Poor emotional health in children leads to long-term mental health problems, poorer educational attainment and has a considerable economic burden.”

Professor Prathiba Chitsabesan, NHS England’s associate national clinical director for children and young people’s mental health, said the return to school may cause anxiety for some pupils as well as those who remain at home feeling isolated or left out.

She stressed that NHS mental health services remain available for children and young people.

“Children and young people may be experiencing a variety of feelings in response to the coronavirus pandemic, including anxiety, distress and low mood, and it is important to understand that these are normal responses to an abnormal situation,” Prof Chitsabesan said.

“The NHS offers a large amount of mental health support for children and young people, and if a child needs urgent mental health support or advice, check nhs.uk for services in your area, including 24/7 crisis support.”

NHS England issued advice on what parents should look out for and steps they can take to look after their child’s mental health.

Signs include finding children are more upset or struggling to manage their emotions, appearing anxious or distressed, increased trouble with sleeping and eating, appearing low in mood, reporting worried thoughts or more bed wetting in younger children.

Parents can help by making time to talk to their children, allowing them to talk about feelings, trying to understand their problems, helping their child do positive activities, trying to keep a routine and looking after their own mental health.

Nadine Dorries, minister for mental health, said: “As many children start to return to school, it’s vital we continue to give them the support they need to maintain their mental health and wellbeing and deal with any feelings of uncertainty or worry they may be experiencing.

“The NHS remains there for those who need it and our mental health services are adapting to best support families and children as we all get used to these changes in routine.”