The children, who are nine, 11, 13 and 14 years old, were born in Attnang-Puchheim in Upper Austria. Their parents are separated and in 2010 their father, who's originally from Pakistan, said he was taking the children on a day trip. However, he never returned them home and later sent his ex-wife a fax saying that he had taken them to Thailand - which turned out to be a lie.
An international arrest warrant was issued for the man, who's now 57, but it took years to track him down. Police worked closely with the Austrian embassy in the Pakistani capital Islamabad.
Last week, the man flew back to Austria with his four children and was immediately arrested at Vienna airport. The four children, a girl and three boys, were taken to a youth welfare centre in Vöcklabruck and reunited with their mother.
Their father, who's now in police custody, told police that he had bought fake Polish passports for the children six years ago and had travelled with them through Hungary, Romania, Turkey and Iran, to reach Pakistan. He found work in Pakistan as a car mechanic.
However, after six years he decided to return with his children to Austria because of the better healthcare and brighter prospects for the children. He told police that he was also afraid that his and his children's lives could be in danger because of the political situation in Pakistan.