(CNN) — Roughly half of the children under 5 years old who were separated from their parents at the border will be back with their moms and dads by a court-imposed deadline Tuesday, but the Trump administration is still not sure when the rest will be reunified.

Still, at a court hearing on Monday, the federal judge who set the deadline for reunifications said he was “very encouraged” thus far.

“There’s no question that the parties are meeting and conferring,” District Judge Dana Sabraw said. “This is real progress and I’m optimistic that many of these families will be reunited tomorrow, and then we’ll have a very clear understanding as to who has not been reunited, why not, and what time-frame will be in place.”

The hearing only covered the roughly 100 children under the age of 5 who were separated from their parents under the administration’s “zero tolerance” border prosecution policy. That group must be reunited by Tuesday under a deadline Sabraw set two weeks ago, when he first ordered the government to put the families back together.

The government still has thousands more children aged 5 and older in its custody that it will have to reunite by July 26 — but the hearing did not cover that group.

Attorneys for the government and the American Civil Liberties Union, which filed the original lawsuit challenging family separations, said they worked together intensely over the weekend to identify the families affected by the deadline and to work out how to move forward.

Justice Department attorney Sarah Fabian provided the court with the most detailed data thus far on the 102 children under age 5 whom it identified as separated from their parents at the border.

Of the 102:

  • 54 will be reunified by Tuesday; their parents are still in government custody and will be released with their children.
  • Two have already been reunified since the initial list was made over the weekend.
  • Six aren’t covered by the order — three because of their parents’ criminal records and three because the accompanying adult turned out not to be a parent.
  • Five are still in ICE custody and could be released soon, but require more follow-up after a background check.
  • Nine have parents who were removed already from the US.
  • Nine have parents who were released already from ICE custody and are somewhere in the US.
  • Four have parents who are in state criminal custody.
  • Eight have parents who are in federal criminal custody.
  • Four could be released to a non-parent sponsor rather than a parent.
  • One there is no information on the parent.

The ACLU, however, said it believes as many as 10 more children might not be on the government’s list, and said it would provide those names to the government to investigate.

The judge ordered the attorneys to file more thoughts by Monday evening on the timelines and procedures for reuniting those parents who will not rejoin their children Tuesday, and the court will hold another hearing Tuesday morning to discuss the issue further.

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