Police will allege in court that the man, An Nguyen from Darlington in Sydney's inner west, exchanged more than 2500 messages on social media with the 13-year-old boy before sexually assaulting him in Bankstown late last month.

When detectives from the Child Abuse Squad were told of the alleged sexual assault, they posed as the boy online and continued a number of online conversations with the alleged offender.

Police say that, during those online conversations, Mr Nguyen arranged another meeting with the boy at Marrickville on Sunday.

Detectives arrested Mr Nguyen at Marrickville railway station just before 2pm on Sunday.

He was taken to Newtown police station and charged with aggravated sexual assault, aggravated indecent assault, inciting a person to commit an act of indecency, procuring a child to produce child abuse material, and two counts of using a carriage service to procure a child for sexual activity.

Mr Nguyen's bail was revoked in the Downing Centre District Court as his mother sobbed in the gallery.

He is next due to appear before court on April 24.

Following the incident, police released internet safety tips for patents, including:

• Be aware of how much time your child spends on the internet.
• Spend time talking to your child about the dangers associated with online conversations.
• Keep the computer in a room the whole family can access; not in your child's bedroom. 
• Consider installing filtering and/or computer blocking software provided by your internet service provider. The Netalert web page provides information on a number of commercially-available products at www.netalert.net.au.
• Ensure you are able to access your child's email and randomly check the contents. 
• Check your phone bill for unusual outgoing calls, or consider using a caller ID device to identify incoming calls.

Tips for children include:

• Do not send a picture of yourself to anyone you don't know and never place a full profile and picture anywhere on the internet.
• Never give out your personal information including name, home address, phone number or school, over the internet.
• Never arrange a face-to-face meeting with someone you have chatted with on the internet.
• Tell your parents or another adult of any contact that makes you feel uncomfortable.