Pressure has mounted on Saudi Arabia, including from allies, to do more to limit civilian casualties in a 3-1/2 year civil war that has killed more than 10,000 people and pushed Yemen to the brink of famine.
Riyadh leads a Western-backed coalition of Arab states supporting the Yemeni government in fighting against the Iran-allied Houthi movement that controls Yemen's capital.
Saudi Arabia told the child rights panel last week that it was working hard to correct mistaken targeting by its military alliance, but the experts voiced scepticism.
The panel of 18 independent experts, in its conclusions issued on Thursday, took note of the Saudi statement but said that Yemeni children continue to be killed, maimed and orphaned.
At least 1,248 children had been killed and nearly the same number injured in air strikes since March 2015, including dozens killed in a strike on a school bus in Saada province in August, it said.
All sides have carried out attacks on civilian targets in Yemen including homes, medical facilities, schools, farms, weddings and markets, in breach of international law, it said.
The panel voiced concern at "the inefficiency of the Joint Incidents Assessment Team (JIAT) set up by the coalition in 2016 to investigate allegations of unlawful attacks by (Saudi Arabia) and members of the coalition on children and facilities and spaces frequented by children".
"There has been no case, let alone a case involving child casualties, recruitment or use of children in armed hostilities, where its investigations led to prosecutions and/or disciplinary sanctions imposed upon individuals, including military officials of (Saudi Arabia)," it said.
The panel called for lifting the coalition's aerial and naval blockade which it said has deprived millions of Yemenis of food and other vital supplies, mainly through Hodeidah port.
In March, another U.N. rights panel called on Saudi Arabia to end discriminatory practices against women, including its pervasive system of male guardianship.