South African border officials say they have intercepted a group of more than 440 unaccompanied children who had travelled from Zimbabwe.
The Border Management Authority (BMA) said the children, all aged under eight, travelled on dozens of buses on Saturday.
It added that they were without parents, guardians and the permission letters required by law.
Reports say the children were visiting parents who work in South Africa.
On social media platform X, the BMA said officials "stopped and searched 42 buses at the Beitbridge border post and found about 443 children under the age of eight who were travelling without parents or guardians being trafficked into South Africa.
"We denied them entry and activated the Zimbabwean officials to process them back into Zimbabwe."
Over a million Zimbabweans live and work in South Africa, and it is believed the children were going to join their parents for the Christmas holidays.
However, the bus drivers told authorities the children were travelling to sport events.
The chairperson of the Africa Diaspora Forum, which represents foreign nationals living in South Africa, said some of the 443 children were travelling with their grandparents.
Ngqabutho Mabhena told his YouTube channel that parents of these children had contacted him with this information.
"This explains why on the Zimbabwean side of the border they were cleared," he said.
Mr Mabhena urged Zimbabwean parents in South Africa not to let their children get on buses unaccompanied or without the proper paperwork.
He said: "Never give your children to a stranger… let us be responsible parents and not put our children in a difficult situation."
South Africa has grappled with an uptick in illegal migrants entering the country through its northern border with Zimbabwe.
Immigration is one of South Africa's most pressing political issues.
Border management has become disorganised and there is pressure on the government to do more about the number of people coming into sub-Saharan Africa's most developed country.
In October, President Cyril Ramaphosa launched a new border force in an effort to cut illegal immigration from Zimbabwe and other countries.