Joseph Parkin was serving a suspended sentence for sex offences and was the subject of a court order banning him from having contact youngsters when he carried out his latest offences.
A judge refused to sentence Parkin when he appeared before Leeds Crown Court because of his concerns over the number of sexual offences the 23-year-old has now committed.
Judge Andrew Stubbs QC ordered that Parkin undergo a psychiatric assessment before sentencing.
He said: "My reading of this case is that the defendant can't stop himself."
Robert Stevenson, prosecuting, said Parkin was made the subject of a sexual harm prevention order (SHPO) in 2017.
In June this year he was handed a suspended sentence for breaching the order by leaving voicemails for girls aged 13 and 14.
The court heard Parkin continued to offend and defied the order almost immediately.
During the same month he wrote his mobile phone number on the back of a bus seat.
The number was seen by a 14-year-old girl who rang Parkin.
Parkin then spoke with her and her 13-year-old friend.
Parkin made sexual comments to the girls and later sent text messages on WhatsApp.
The defendant then began following the two girls.
One of the victims told her grandmother that Parkin had been following them.
The following day the girl's older sister confronted Parkin in the street as he followed the girls and he rode off on his bike.
Police were contacted and Parkin refused to comment during an interview.
Parkin pleaded guilty to engaging in sexual communication with a child and two counts of breach of a SHPO.
He has 17 previous convictions for sex offences or breaching SHPOs.
Parkin was first convicted for sexual assault of a child under 13 in 2014 and was given youth rehabilitation order.
He also has convictions for inciting a girl under 16 to engage in sexual activity and causing a child under 13 to watch a sexual act.
Judge Stubbs adjourned the case after hearing the prosecution opening of the case.
Parkin will be sentenced on January 31 next year after the completion of the psychiatric report.
Parkin, of William Prince Grove, Belle Vue, Wakefield, appeared in court via a videolink from prison.
The judge told him: "I know you probably want to know what is going to happen to you today, but I am at a stage where I am really worried about the way you keep offending with young children and I am trying to think of the best way to deal with you."