Bombs and bullets, natural disasters, child marriage and discrimination - these are just some of scary realities that keep children out of school.
It's Halloween - when children in many countries dress up and enter the spooky world of ghosts and witches.
The celebration is all about having fun. But there are genuine reasons for many children to be scared today and every other day.
Millions of them live with the spectre of such horrors as war, attacks on schools, bullying, discrimination, being married young or working in dangerous jobs when they should be safe at school and learning.
On a day when girls and boys like to be scared just a little, we look at some of the real nightmares and traumas that children have to endure and which contribute to 263 million of them being out of school.
Bullets and bombs
More than 21,000 students and teachers in 41 countries were harmed in attacks on schools and universities around the world over a five-year period, according to the Education Under Attack 2018 report.
A separate UN report in June said crises unfolding in Central African Republic, the Democratic Republic of the Congo, Myanmar, South Sudan and Yemen had meant rising violence against school children - with 10,000 killed or maimed in 2017.
An estimated 158 million school-age children and adolescents are living in over 20 countries and areas currently affected by armed conflict. Millions have had their education disrupted by wars and conflicts in the past year.
About 12 million girls a year are married before the age of 18 - often to much older men and with devastating consequences for their health and education.
Poverty is often the main reason for child marriage but protracted conflicts, natural disasters and cultural beliefs also put girls at risk.
The UN is aiming to end the practice by 2030. About 25 million early marriages have been prevented in the last decade, with the biggest decline in South Asia, where the risk of a girl marrying before her 18th birthday has fallen from 50% to 30% in recent years.
Disasters displaced 18.8 million people in 135 countries last year. Of these, 8.6 million were triggered by floods and 7.5 million by storms, especially tropical cyclones.
They included hundreds of thousands of children whose education was stopped or disrupted due to schools being severely damaged or destroyed by the extreme weather conditions.
The South Asia floods in 2017 destroyed or damaged 18,000 schools and left 1.8 million children out of education.
Much social and cultural discrimination remains around disability. Children with disabilities are more likely to miss out on school than other children.
An estimated one in three out-of-school children have a disability - and throughout Africa, less than 10% of children with a disability are in primary education.
For children who are already marginalised, such as girls and children living in rural areas, a disability creates an additional barrier to accessing education.
The UN wants to eradicate child labour by 2025. But with millions of children under the age of 18 working, that's going to be a massive task.
Across the world, 152 million children aged five to 17 are victims of forced labour and often miss out on education, according to the International Labour Organization (ILO).
They toil in homes, mines, fields and factories, carry heavy loads, work long hours and suffer exposure to pesticides and other toxic substances.
Unsafe toilets and washing facilities
Nearly half the world's schools lack clean drinking water, toilets and handwashing facilities, putting millions of children at risk of disease, experts have warned.
Almost 900 million children have to contend with a lack of basic hygiene facilities during their education, putting their health at risk and meaning some have to miss school.
In parts of sub-Saharan Africa and other regions, girls can miss out on up to five days of school per month or stop going to school entirely because of insufficient access to water and hygiene facilities, no separate toilets for girls, lack of sanitary supplies and sexual advances from boys in mixed toilets.
South Africa is shutting down "hole-in-the-ground" toilets at state-run 4500 schools after a five-year-old girl fell in one and drowned this year.
Malnutrition and disease
Around 45% of deaths among children under five are linked to undernutrition. Malnutrition (which includes undernutrition) means 52 million children under five are wasted, 17 million are severely wasted and 155 million have stunted growth, according to the World Health Organization.
Six million children worldwide died last year from preventable diseases and other complications - about half the number of similar deaths in 2000 when nations endorsed goals to end extreme poverty.
In 2017, 2.5 million newborns died in their first month. A baby born in sub-Saharan Africa or in Southern Asia is nine times more likely to die in the first month than one born in a high-income country.
Prolonged exposure to high levels of stress from trauma, violence, neglect or deprivation is called toxic stress and can have devastating physical and psychological consequences for children.
Trauma affects their ability to learn and to stay in school. It can prevent or slow the healthy development of the brain - and that can have massive effects on the rest of a child's life.
More than one million babies are born each year in conflict zones - including Syria, where UNICEF warned that relentless violence and terrible living conditions are "having a devastating impact on the protection of children of all ages".
Being displaced from home
Almost 70 million people around the world have been forced to flee their homes by conflicts and other traumatic situations. Among them are nearly 25.4 million refugees who have gone to other countries - over half of them under the age of 18.
They have been uprooted from their friends, schools and sometimes even their families. They face perilous journeys to reach safety, often having to live in camps.
Some displaced children never return to school. They are at risk of child labour, early marriage, recruitment and other forms of exploitation.
Recruitment as child soldiers
Children - including girls - have been used in wars in at least 18 countries since 2016, says Child Soldiers International.
More than 20% of the 197 UN member states still enlist children into their militaries, including 17 states which enlist as young as 16. About 19,000 child soldiers are still serving in South Sudan - although a few hundred have been freed this year.
Child Soldiers International says some child soldiers are used for fighting – to kill and commit other acts of violence. Others are used as cooks, porters, messengers, informants or spies, and for sexual purposes.
Pregnancy and childbirth
In many parts of the world, girls who are pregnant - regardless of their circumstances - will be excluded from school.
Many do not return after giving birth due to those rules, stigma, fees, lack of childcare and the unavailability of flexible school programmes.
About 16 million girls aged 15 to 19 and some one million girls under 15 give birth every year - most in low- and middle-income countries, according to the World Health Organization. Young girls are more likely to have premature babies and to have complications during labour.
Bullying and gang violence
Millions of schoolchildren are victims of assault, bullying and punishment - and that can leave them with long-term educational and mental issues.
A 2017 report found that an estimated 1.7 billion boys and girls - that's three in four - suffer mental or physical abuse each year, including being physically punished at home.
Gang violence on the way to school or even inside school can make children vulnerable. In many Latin American countries in particular, fear of violence means families often keep their children home.
Dangerous journeys to school
A simple walk to school can be extremely unsafe or intimidating for some children. Many parents refuse to send their children - particularly girls - to school in case they are harassed, exploited or sexually abused.
An estimated 246 million girls and boys are harassed and abused on their way to and at school every year - with girls particularly vulnerable.
Many children in remote communities also have to make the most unimaginable and dangerous journeys every day to access education. Some walk along treacherous cliff edges. Others trek into the mountains for miles or cross broken bridges to be at school on time.