Sullivan even bought the youngster a pair of trainers as a reward when the pair slept together for the 100th time, Teesside Crown Court heard.
She first seduced the boy by plying him with alcohol and performing a sex act on him, the court was told.
The pair went on to have a ten-month affair, which was only uncovered after rumours circulated at the boy’s school about Sullivan being pregnant.
Investigators also discovered the schoolboy had been boasting to friends in internet chatrooms about his relationship.
The mother would often have sex with the youngster in her Middlesbrough home after sending her own son to stay with his grandparents.
When police arrested Sullivan in October, they found a diary filled with childish entries and 191 stars to mark each encounter.
She initially denied having sex with the boy and tried to explain away some of her diary entries – such as ‘Angela loves (the boy’s name)’ – as innocent scribblings.
But when she appeared in court yesterday, Sullivan admitted ten specimen charges of causing or inciting a child to engage in sexual activity – one for each month of the affair.
Her case was adjourned and Sullivan was remanded in custody so psychiatric and probation reports can be drawn up.
She will return to Teesside Crown Court to be sentenced next month.Lawyer Andrew Turton, defending, applied for the psychiatric report.
Judge Tony Briggs said: ‘I think that is likely to be necessary.’
Sullivan, who has no previous convictions, faces being placed on the sex offenders register.
She could also be jailed indefinitely for the protection of the public.
Several windows at the unemployed mother’s home have been smashed since she was arrested.