Man charged after train attack on baby

A 10-month-old boy was allegedly pricked with a safety pin and hit with a mobile phone during an attack by a man on a train on the NSW Central Coast.

The baby, who suffered head injuries, was travelling with his mother and a 22-year-old man on Wednesday night when a number of people witnessed the alleged assault and alerted police.

Officers boarded the train at Woy Woy station to find the boy strapped in his pram in a distressed state, Brisbane Water local area commander superintendent Danny Sullivan said.

They arrested the man and charged him with one count of assault occasioning actual bodily harm.

He was refused bail at Gosford Local Court on Thursday and is due to face Woy Woy Local Court on August 9.

The baby boy has been treated at Gosford Hospital and placed in the care of the Family and Community Services Department.

Supt Sullivan said he has nothing but praise for the passengers "who had the courage to do the right thing" by reporting the alleged assault.

"Those people have made a difference to that defenceless boy's life," he told AAP.

Supt Sullivan said the case served as a reminder to the community to "rightfully" speak up against domestic violence.

"There's no such thing as a bystander. We all have an obligation," he said.

Police would not confirm if the man was in a relationship with the boy's mother.