An eight-year-old girl told her mother she had been raped by two boys aged 10, the Old Bailey has been told.
The girl had been playing with her younger sister but said she had been taken to a block of flats and a field by the boys, it was alleged.
When the younger girl went home without her sister, the mother went looking for her and found her with the boys, said Rosina Cottage, prosecuting.
The boys, now aged 11 and 10, who cannot be identified for legal reasons, deny two charges each of rape and two charges each of attempted rape of a child under 13, in October, last year.
The offences were alleged to have happened in Hayes, west London, near to where all the children - who knew each other - lived.
The boys, amongst the youngest charged with rape, looked tiny sitting in the middle of the court between their mothers and solicitors.
The judge, Mr Justice Saunders, and lawyers in the case dispensed with their robes and wigs.
The jury was told that sitting hours had been shortened and other steps were taken because the defendants were so young.
The judge, wearing a dark grey suit, sat where the court clerk normally sits so he was on the same level as the boys.
Miss Cottage told the jury of six men and six women: "This case concerns rape by two boys still at primary school of a girl even younger than them."