Washington (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 at the border. 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.

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