It may take federal officials two years to identify what could be thousands of immigrant children who were separated from their families at the southern United States border, the government said in court documents filed on Friday.

A federal judge had asked for a plan to identify these children and their families after a report from government inspectors in January revealed that the Trump administration most likely separated thousands more children from their parents than was previously believed.

These families were separated before the administration unveiled its “zero-tolerance” immigration policy in the spring of 2018, when nearly all adults entering the country illegally were prosecuted and any children accompanying them were put into shelters or foster care.

To identify these families, the government said it would apply a statistical analysis to about 47,000 children who were referred to the Office of Refugee Resettlement and subsequently discharged, according to the court filing. From there, the government said it would manually review the case records of the children who appeared to have the highest probability of being part of the separated families.