After pleading guilty and being sentenced to a three-month jail term on Wednesday, the man was due to be released from custody that night after already serving 115 days in custody.

Gregory Pace was in a drug-induced psychosis when he stepped in front of the girl and held her bicycle in a Seddon street, leaving her distressed and crying, Melbourne Magistrates Court heard.

A woman who witnessed the incident went to the girl's aid and helped calm Pace and return the girl to her father, until Pace sexually assaulted the woman by grabbing her body and trying to lift her dress, prosecutor Amitoj Singh said.

He also exposed himself to the woman and walked down the street with his pants down, exposing himself to residents.

The girl was riding about 50 metres ahead of her father and siblings when Pace grabbed her bike on September 11 last year, Acting Sergeant Singh said.

He did not touch the girl and she didn't witness the woman being assaulted, the court heard.

Pace, who has five sex offence convictions dating back to 2005, was on Wednesday jailed for three months after pleading guilty to sexual assault and exposing himself in public.

But with 115 days in prison already served, the 40-year-old was due to be released from custody that night and begin an 18-month community corrections order.

Defence counsel Lorien Ruane said Pace grabbed the girl's bike in the belief there was a fight at the end of the street, and that he held on to prevent the child falling in the gutter.

But he acknowledged he would have frightened the girl and was remorseful. "It wasn't an aggressive act, it was a protective one," Ms Ruane said.

Pace has a history of substance abuse, the court heard, but was determined not to use drugs again and was now in a committed relationship with a woman.

When magistrate John Bentley asked where the woman was, Ms Ruane said the woman was in the Philippines and had met Pace online.

She planned to come to Australia after a bout of heart surgery, the court heard. "Are you telling me this is serious?" Mr Bentley asked of the relationship.

When told the woman knew of Pace's past the magistrate told him: "You are an individual she should run a mile from."

Pace also pleaded guilty to exposing himself at Altona train station on May 15, 2016 when he pulled his pants down at a CCTV camera when told over an intercom that the trains weren't running and he had to catch a bus.

And he admitted to failing to alert police in 2016 that he had opened new social media accounts when required to do so as a registered sex offender.

Pace must undergo treatment for sex offenders and regular drug testing and treatment as part of his community corrections order.

"I am over it. I want help. I want to settle down in my life," he said. "I want to get out of jail and start a new life ... I am a man and I want to be a proper citizen."