A man has been charged over two separate sexual acts allegedly committed towards children in a library and on a train.
Police will allege the man went to the library in Windsor about 2pm on Saturday, August 17 and committed a sexual act in front of two 16-year-old girls.
Officers were notified and a second offence then occurred the following week, a police statement said.
"About 6.20am [on] Friday, August 23, a 13-year-old girl boarded a train at Quakers Hill and travelled to Riverstone when a man boarded and sat next to her," the statement said.
"It is alleged the man committed a sexual act while sitting next to the girl.
"The teen left the train at Mulgrave where she met with her mother and police were contacted."
Police attended Richmond Railway Station and arrested a 40-year-old man.
He was taken to Windsor police station where he was \charged with intentionally inciting a child aged 10 to 16 years to do a sexual act to them, carry out a sexual act with another person without consent, and wilful and obscene exposure in a public place.
The man was refused bail and appeared in Parramatta Local Court the following day.