He told the victim's mother he would take the 8-year-old to her grandmother's house but on the way stopped to get a pizza and took her to Halswell Domain instead.
In the parked car, he showed her pornography before pulling out his penis and asking her if she wanted to touch it, which she declined.
He then said because he had shown her his penis she needed to show him her vagina, which she did. He told her not to tell anyone.
Mein met his second victim in November 2021 when he befriended her on social media.
The victim's father became aware of this and told her to block Mein, which she did but later unblocked him and the pair began communicating, even setting up alternative accounts to talk to each other in secret.
His offending against her took place between February and May this year, when the girl was aged 12 and 13.
When police examined Mein's phone they found messages between the two engaging in sexual conversations with the victim calling him "hubby" while he called her "beloved".
The pair would video call each other and Mein would ask the victim to perform sexual acts for him which he would record and take screenshots of.
Judge Gilbert said it appeared that Mein and his victim believed they were in a relationship with each other.
"It's clear you felt you were in a relationship with [the second victim] which is completely distorted given your age gap - she was just a girl."
Mein would meet with his victim while she was on lunch break at school and they would kiss and fondle each other.
On one of those occasions Mein took condoms with him in hopes he and his victim would have sex. He also gave her a cuddly toy and a ring as a gift.
Mein's lawyer Jessica Bibby said he was remorseful and willing to engage in rehabilitative processes and had genuine concern for his victims.
She said his guilty plea should be taken into account upon sentencing and the fact that he has no prior convictions.
The Crown said a term of imprisonment was appropriate for this "serious offending". They said Mein lacked understanding of some of his offending and sometimes saw himself as a victim.
Judge Gilbert acknowledged the presence of some family members of the victims in court.
"What you have done has a had a massive impact on the lives of these kids and their families," she told Mein.
He said aggravating factors that made Mein's offending worse was the substantial age gap between him and both victims, the harm caused, the premeditation and grooming that went into the offending, the documenting video calls through screenshots and recording software, the number of offences and the fact there were two victims.
Judge Gilbert said Mein would be registered on the child sex offender register and imposed an end sentence of 3 years and 11 months.
