Many schools in Liberia have reopened after a six-month closure caused by the deadly Ebola outbreak.
Monday's move comes a day after the leaders of Liberia and Sierra Leone vowed to eradicate the virus, which has killed more than 9,000 people, mainly in West Africa, by mid-April.
Teachers have been trained to implement and monitor safety measures, while soap and other hygiene materials have been distributed and mass mobilisation campaigns on Ebola prevention have been conducted nationwide.
Pupils who trickled in to Saint Michael High School on the outskirts of the capital washed their hands with chlorinated water before going inside.
"I feel happy to come to school today because for so long I have not seen my friends," Albert Kollie, 18, told the AP news agency.
"I am very happy to be counted among the living and I pray that Ebola be eradicated from this country.
"I am not afraid because everyone in Liberia today knows the danger called Ebola.
"No one wants to die so we have no choice but to respect the rules given by health authorities."
Ebola, one of the deadliest known pathogens, is spread through direct contact with the bodily fluids of an infected person showing symptoms such as fever or vomiting.
Liberia has seen the highest death toll from the epidemic, with at least 3,800 killed.
In neighbouring Guinea, where the outbreak began, schools already have reopened though many fearful parents have kept their children home.
In Sierra Leone, where disease transmission is now the highest, officials hope to reopen schools by the end of March.
All three countries have seen a dramatic drop in infections compared with the peak of the epidemic in September and October.
UNICEF said it was too early to be able to have a clear overview of how many schools had opened across Liberia.
"This will happen gradually from today. Typically it can take up to a month before the majority of students are back in the classroom," a spokeswoman in Monrovia told the AFP news agency.
"Throughout that period education authorities will be working to ensure that conditions are as safe as possible."
UNICEF and its partners are handing out more than 7,200 hygiene kits for more than 4,000 Liberian schools, and training 15,000 teachers and school administrators in monitoring of safety protocols.
"UNICEF is supporting the ministries of education and health in our common goal of seeing all Liberian children back in school as soon as possible and as safely as possible," said Sheldon Yett, UNICEF's representative in Liberia.
"The provision of thousands of these kits, and ongoing training on the protocols is part of our commitment to the children of Liberia."
Meanwhile, the International Rescue Committee aid agency said it was providing training in some of the worst hit areas of Monrovia, where people are still contracting Ebola.