The paedophile groomed his victim via a fake profile on Facebook.
Kelsey had a previous conviction for sexually assaulting a 13-year-old girl before he targeted his Scottish victim.
The Scots girl’s mum has said social media companies must do more to stop teens being groomed.
She has backed the NSPCC’s call for the UK Government to press ahead with an Online Harms Bill to force tech firms to keep children safe on their sites, with tough consequences if they fail to do so.
She said: “It’s far too easy for anyone to set up a fake profile on social media, which allows them to hide their real identity and gives them access to millions of children.
“The tech giants claim the internet is too big to police, but if they were held liable and fined huge sums when children came to harm, I’m sure they’d find a way.”
The mum also wants the Crown to appeal against Kelsey’s “paltry” two-year sentence, imposed at Falkirk Sheriff Court last week, and wants to know why the case was not prosecuted at the High Court.
She said: “He has spent eight months on remand. He’ll be out at half-sentence after another four.
“For six months, my daughter only left her room to come and get food. She has self-harmed and been suicidal and shows little sign of recovery.
“He will soon be free to get on with his life while she is left serving the life sentence.
“We can’t understand why this was a sheriff court case. The law says a girl of 14 can’t give consent, yet he wasn’t charged with rape.
“What message does that send other victims about how seriously we take these offences?
“It also gives paedophiles the message that they can carry on their habit as any punishment won’t be so bad.”
Unmarried Kelsey, a director of his own car sales company, appeared in court by video link from Low Moss Prison, near Glasgow, where he had been held since his arrest by Humberside Police in January.
He pled guilty to having sexual intercourse with the girl and sending her sexual communications from March 2019 to January 2020.
In October 2012, Kelsey, then 24, was spared jail at Hull Crown Court after having groomed and initiated sexual contact with a girl of 13 he was teaching to play piano.
The judge heard that Kelsey had befriended the girl on Facebook and initiated secret contact, urging her not to tell her parents.
The judge, who added that Kelsey’s behaviour was unlikely to be repeated, heeded a plea from the victim’s parents not to jail him – a plea they made because their daughter was refusing to talk to them for reporting Kelsey.
Kelsey was sentenced to a two-year community order that included taking part in a sex offenders’ treatment programme and was placed on the sex offenders’ register for five years.
Just weeks after coming off the register, he was caught by a vigilante group, Stop, trying to arrange to meet a nine-year-old girl.
The group called police and posted footage online as they waited for him to be arrested, but he was not prosecuted.
Three weeks later, Kelsey made his first contact online with his Scottish victim.
Her mum said: “He clearly has a problem that is not going away, and a two-year sentence, which really only means one year, means he won’t be able to do treatment programmes in jail, especially as he’s already been on remand for eight months.
“He will come out early next year the same way he went in and will be a danger to other girls, and as we saw from the girl he was grooming before my daughter, even nine-year-olds aren’t safe from him.”
A Crown Office spokesperson said: “As with all cases, the Crown will consider the sentence and give consideration to whether it might be unduly lenient.”
A spokesperson for children’s charity NSPCC Scotland said: “This case highlights how social media apps such as Facebook Messenger can give sexual offenders looking to target children an easy gateway to their victims.
“This is not a problem that law enforcement can tackle alone; it is vital that tech firms take responsibility for protecting young people on their platforms.
“The NSPCC is calling on the UK Government to press ahead with an Online Harms Bill that will force these companies to keep children safe on their sites, with tough consequences if they fail to do so.”