Children's charity Barnardo's asked 4,000 children and young people aged eight to 24 how they'd been feeling during the coronavirus pandemic.
At least a third said they'd experienced an increase of mental health and wellbeing issues like stress, loneliness and worry, with boredom and feeling trapped also among the main emotions they'd felt.
Most said they missed going into school or college and a third also said they had more trouble sleeping, which could have a knock on affect on school work, behaviour and family life.
Barnardo's also found many young people were struggling because the things that help them stay well aren't available now, or the lockdown was making existing difficulties even harder.
A lack of social contact and being 'hidden' from teachers and other trusted adults adds to the significant risks these young people already experience.
Barnardo's says it welcomes the government's recent announcement of £1bn to help vulnerable children catch-up on their missed education but it wants more investment to support children and young people with their mental health and wellbeing too, not just academically, and says that this support should be available over the summer holidays as well as during term time.
Earlier this month the government announced it would be providing new online resources and more than £750,000 in charity grants to help schools and colleges deal with the impact of coronavirus on mental health and wellbeing. It says this adds to the support already put in place during the pandemic, including more than £9 million invested in mental health charities to help them reach those most in need,