It appeared to mark a breakthrough after two weeks in which the Freemen had no contact with the FBI. At the weekend, agents cut off electricity to the remote ranch in the first move to step up the pressure on those inside, and a new round of talks ensued.
The Freemen, a motley group of about 18 people led by a bankrupt rancher and united by their rejection of all government authority, have kept the FBI at bay since agents arrested two leaders and surrounded the ranch on 25 March.
About a dozen people inside are wanted on fraud charges, concerning the issuing of fake money orders, cheques for millions of dollars and the making of threats. Though they are routinely spotted carrying high-powered rifles, they are not accused of any violent crimes.
The departure of the two girls - Jaylynn and her elder sister Courtnie Ward - had been the main goal for a series of negotiators who have failed to talk the Freemen into giving up. Another girl, Ashley Taylor, 16, is believed to be the only minor still inside.
Some observers believe the presence of children at the ranch would have greatly complicated the task for the FBI's tactical teams as they looked at ways to bring an end to the longest siege of its type in US history.
Heavily criticised over their handling of two earlier episodes - at Waco, Texas, and at Ruby Ridge, Idaho - where casualties included children, federal agents have handled the Freemen with extreme caution from the beginning.
Amid mounting impatience with an operation reportedly costing close to $100,000 (pounds 65,000) a day, local residents on Thursday were due to present a petition with 200 signatures calling on authorities to use "reasonable force".
The girls' mother, Gloria Ward, was described as a member of a breakaway Mormon sect that believes girls are ready for marriage at puberty. She sought the refuge at the ranch, dubbed the Justus Township by the Freemen, after her former husband in Utah had won a custody order for Courtnie. An older daughter, Leslie, is already in state care.
James "Bo" Gritz, a decorated Vietnam veteran and a figurehead for far- right groups, was one of those who tried to negotiate the release of the children.
After visiting the compound last month he described them as chewing meagre rations of cracked corn. He said it was clear that the Freemen leaders knew "the value of placing children between themselves and the FBI". The FBI cut off power to the Freemen on Monday. Although they are said to have their own electrical generator and supplies of diesel fuel, only two dim lights were seen in the compound at night.
Armoured cars were openly moved into positions close to the ranch this week. However, officials also sent out signals that they were prepared to play the waiting game for months more if necessary.
On Wednesday night, in one sign that the harder line was beginning to take effect, rancher Edwin Clark emerged for two hours of talks with FBI negotiators before returning to the ranch. Three FBI agents in two vehicles entered the compound yesterday morning.
They emerged several hours later with the children, their mother and her husband, Elwin Ward, before they were all escorted to an FBI command post 30 miles away.