Many infant school children are showing signs of mental health issues such as anxiety, panic attacks and depression, according to a poll of teachers.
In one case, a teacher described an eight-year-old pupil who climbed on the roof and said they wanted to kill themselves.
The poll, carried out by the NASUWT teaching union, suggests that the vast majority of school staff believe that they come into contact with pupils, of all ages, that are suffering from mental health problems.
The research also found that many teachers are aware of sexual harassment among students, and youngsters sharing sexual messages, photos and videos.
Overall, 96% of the more than 1,300 union members questioned said that they believe there are pupils that they come into contact with that are experiencing mental health issues.
Of these, around one in seven (14%) said that pupils experiencing these difficulties were aged between four and seven (infant school pupils), while over a quarter (27%) said they were aged seven to 11.
The age group that teachers were most likely to say were affected by mental health issues were those age 11 to 16 (68%).
Some 1% said that children under four were affected.
Asked about the type of mental health issues children are suffering from, around 92% cited anxiety and panic attacks, while 80% said depression.
In addition, around 67% said youngsters were self-harming, while 49% said eating disorders and 45% said pupils were showing signs of OCD.
One member told the union: "Access to mental health services is appalling for young children - a young child climbing onto a roof and saying they wanted to kill themselves (aged eight) was not deemed serious enough to get CAMHS (Child and Adolescent Mental Health Services) support."
The poll also found that 86% are aware of pupils they teach sharing messages, photos and videos or a sexual nature, while over a third (38%) were aware of youngsters sexually harassing other pupils, and a similar proportion (39%) said they were aware of youngsters being sexually harassed by other youngsters.
NASUWT general secretary Chris Keates said: "Teachers have never before had to deal with such a complex range of pupil welfare issues as they do today.
"The pressure on teachers and headteachers is enormous and is putting at risk their own mental and physical health and wellbeing."
A spokesperson for the Department for Education said: "We want all young people to grow up feeling confident about themselves and able to get the right mental health support when they need it.
"We have pledged £1.7 billion to improve the mental health services on offer to children and young people.
"But we know there is more to be done to ensure progress in this area, which is why we have recently outlined proposals to improve links between the NHS and schools, provide quicker access to intensive support and more capacity to be able to intervene earlier."
On Saturday, another revealed that almost one in 10 teachers in England have been sexually harassed by a pupil, while several had "upskirt" images taken of them in the workplace.