Christopher Morrison preyed on the child while his mother, grandmother and aunt waited for the youngster outside the men’s lavatory at the Asda store in Britannia Way, Clydebank, West Dunbartonshire.
Lord Bracadale told Morrison, now 20, at the High Court in Edinburgh yesterday: “You pled guilty to a very disturbing offence committed on a boy in a public toilet.”
The judge said a victim impact statement completed by the youngster’s mother revealed the child was affected by what had happened.
Lord Bracadale told Morrison: “You have no previous convictions, but it is clear from the risk assessment report there is a serious background here.”
The judge ordered that Morrison should be kept under supervision for a further three-and-a- half years.
Morrison’s counsel, Kevin McCallum, said his client was participating in programmes to address his problems.
The sexual assault on the boy on 18 September last year prompted a high-profile appeal to catch the attacker. Police detained Morrison, who was 19 at the time, days later at his home in Elderslie, Renfrewshire.
Unemployed Morrison later admitted committing the sex attack on the child, who cannot be identified.
Advocate depute Bruce Erroch said the youngster had been at a cafe at the supermarket with relatives when he needed to go to the toilet about 1pm. Morrison was already in the lavatory when the child walked in and he lifted the youngster up in what the victim thought was an attempt to help him.
But the attacker performed indecent acts on the four-year-old. The prosecutor said: “He did not say anything to the victim while doing this, but put his finger to his own mouth, which the boy took to be a gesture to be quiet.”
When the boy emerged, his mother noticed his zip and belt were still undone and, as she fastened them, the child revealed that a man had done something to him.
Morrison had fled by the time police arrived but they were able to identify him from CCTV footage and descriptions.
He was interviewed with an appropriate adult present as police thought he might have learning difficulties but made no relevant admissions. DNA samples taken from the victim were found to provide a match with Morrison.
Morrison was also placed on the sex offenders register.