This happened 10-15 times, with the girl receiving money, alcohol and cigarettes in return.
In June 2019, the first girl introduced the second girl, who knew about her transactions with Hyslop, to him.
The girl, who was 15 but told Hyslop she was 17, performed oral sex on Hyslop in exchange for cigarettes and alcohol.
The girls left, but Hyslop asked the 15-year-old to come back — when she did, they had intercourse.
Hyslop's offending came to light after the second girl disclosed to a support worker what had happened.
Hyslop earlier pleaded guilty to two representative charges of contracting for sex with someone aged under 18, a Prostitution Reform Act offence.
Crown prosecutor Richard Smith said there had been a grooming element to Hyslop's offending. Although the case was finely balanced, to denounce Hyslop and protect the community from him, a custodial sentence was appropriate.
For Hyslop, Steve Turner said his client had had an extremely traumatic upbringing, which was a factor in his behaviour.
He was remorseful and had apologised for his actions.
Judge Michael Turner said Hyslop's offending was against two highly vulnerable young people, and Hyslop had known they were living in an Oranga Tamariki home.
While the first girl had no issues with Hyslop and had excused his offending, that demonstrated her extreme naivety, the judge said.
The second girl had suffered serious consequences as a result and was still affected.
Judge Turner accepted Hyslop had insight into his offending and was obtaining counselling, and the mitigating factors of the case meant he came to a sentence of 18 months' imprisonment.
Judge Turner said the same finely balanced issues which brought the case below the two-year level above which home detention could not be considered were also in play in the decision whether to jail Hyslop.
The work he had already done, and the fact his proposed home detention address was in another location, meant home detention was a suitable but still severe enough punishment, Judge Turner said.
