Children over 15 years are tried as adults and can be executed, "after trials falling short of guarantees of due process and a fair trial", according to the report by the UN Committee on the Rights of the Child.
The committee's 18 independent experts analyzed the kingdom's compliance record with a UN treaty protecting the rights of citizens under the age of 18.
Experts voiced concern that the Saudi government "still does not recognize girls as full subjects of rights and continues to severely discriminate (against) them in law and practice and to impose on them a system of male guardianship".
The committee said violations of young girls' right to equality should not justified using traditional, religious or cultural attitudes.
Children from the minority Shi'ite community and other religious minorities are continually discriminated against in their access to schools and justice in the Sunni-ruled kingdom, they said.
According to the UN committee, out of 47 people executed on 2 January for security offences, four were under 18.
Responding to the committee's findings, the Saudi Human Rights Commission told the body that Islamic Sharia law, was above all laws and treaties, including the Convention on the Rights of the Child.
Bandar Bin Mohammed Al-Aiban, the chairman of the Saudi Human Rights Commission, did state the kingdom had the political will to protect children.
All sexual abuse against children should be made illegal in Saudi Arabia with persecutors prosecuted, the experts said.
The case of Muslim preacher Fayhan al-Ghamdi was cited by the report, saying his charges were reduced and he was released from jail "after having raped, tortured and killed his five-year-old daughter" in 2012.
Saudi air strikes in Yemen were also strongly criticized by the UN watchdog which said hundreds of children had been killed and maimed, Independent reported.
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