Ahed, who turned 17 behind bars last month, was denied bail by the military court judge and stands little chance of winning her case as such courts have a 99 percent conviction rate. The closed-door trial is based on 12 charges including those of aggravated assault and incitement.
Tamimi's mother, Nariman, and cousin Nour, 20, were also due to go on trial later Tuesday.
Earlier in the day, Tamimi's father told The Associated Press as he headed into the court that he came "with no good expectations, because this a military court, and it's part of the Israeli military occupation".
"The Tamimi family - which may not be a real family - dresses up kids in American clothes and pays them to provoke IDF troops on camera".
The UN experts also said that "her place of detention - Hasharon prison in Israel - [is] in violation of the Fourth Geneva Convention which states that the deportation of protected persons from occupied territory to the territory of the occupying power, or to that of any other country, is prohibited, regardless of the motive".
Ahed Tamimi, then 16, was recorded by her mother shoving and shouting at two Israeli soldiers in the driveway of her family home in Nabi Salih in the West Bank on December 15, 2017.
She was arrested during a night raid four days later, after a video of her threatening and beating two Israel Defense Forces soldiers went viral. In contrast, Israelis enjoy the benefit of urban freedom and prosperity in an atmosphere of normalcy with relatively high levels of security in recent years that has greatly diminished the security threat, and in the process, effectively erased Palestinian grievances and aspirations from public consciousness.
"Prisoners held on administrative detention in Zionist jails chose to boycott Israeli courts in a final and unprecedented manner... to protest this unjust policy", Issa Qaraqe told a press conference in the West Bank city of Ramallah.More news: Gay Olympic medalists pose for picture and send message
In this January 4, 2018 file photo, demonstrators hold posters reading, "Release Ahed" during a protest demanding Israel to release Ahed Tamimi.
On Tuesday morning Tamimi, wearing prison uniform and with her hands and feet in restraints, was led into the courtroom at the Ofer military prison near Ramallah for preliminary trial hearings.
Ahed Tamimi is one of some 350 Palestinian children now in Israeli military detention. She said she is still waiting to receive case material from the prosecutor, that her client did not enter a plea and that the next hearing would be March 11.
After a few minutes, the judge suddenly ordered all spectators except family members to leave and announced that the proceedings would continue behind closed doors.
The case has triggered a debate between those who see the girl as an icon of resistance and others who perceive her simply as an attention-seeking youth.
United Nations human rights experts said Tamimi's continued detention violates worldwide legal standards.
"The Convention on the Rights of the Child, which Israel has ratified, clearly states that children are to be deprived of their liberty only as a last resort, and only for the shortest appropriate period of time", Michael Lynk, the United Nations special rapporteur on the situation of human rights in the Palestinian Territory occupied since 1967, said Tuesday after Ahed's first hearing in which the court made a decision to ban media from the trial.