Dublin Children's Court had earlier heard he had changed his plea to guilty. Judge Paul Kelly heard evidence and adjourned the case for a probation report on the boy to be furnished to the court.
The schoolboy, now 14, faces five counts of sexual assault as he cycled past them in two residential areas on three dates in March and April last year in the city's north side.
Three incidents happened on the same day.
Detective Garda Alan Davis outlined the facts. On the first occasion, the boy on his bicycle approached a woman from behind in a park.
The woman was "smacked in the bum area".
Four days later, at around 9.30 am, he cycled to a jogger in the same area and "smacked her on the bum".
Three hours later, he did it to another woman in the park and afterwards to a girl in her mid-teens.
The court heard gardai arrested him ten days later, and they released him pending a decision on charging him.
However, almost three weeks later, at a second location, he approached a mother on her way to collect her children from a crèche.
He was cycling from behind and "smacked her on the bum".
The boy, accompanied to court by his mother, has no prior criminal convictions.
The detective agreed with defence counsel Amy Deane that special directions were required from the DPP because of the boy's age.
He also accepted that the teenager was vulnerable and became upset when interviewed.
However, the boy also made "some admissions" and apologised, the court heard.
Detective Garda Davis agreed that the incidents were at the lower end of the scale for sexual assaults, quick in nature and occurred while the boy was in motion.
Earlier, the defence handed into court a report from family therapy sessions. Counsel said it detailed "complex issues" in his life.
The boy must obey bail conditions: no contact with complainants, a curfew, and he must stay away from the two areas where the incidents occurred.