Police are advising parents to keep a close eye on their children's social media activity after a series of suspicious posts were made on community pages in Wellington and Auckland.

The posts are from a man seeking children, often aged between nine and 13 years old, to be part of a game that involves so-called "sliming" or "gunging" - pouring custard over themselves and the man.

The man offers money, vouchers or tickets to events in exchange for children playing this game with him.

According to the police, he says this game is part of his training as a youth worker or is related to a project he is completing for tertiary study.

The police said they are investigating the man. They have established he is not training as a youth worker and is not involved in any relevant tertiary study.

"Police request that members of the community do not engage with this person via social media.

"Parents are encouraged to check in with their kids and understand what they are doing online.

"Have a conversation with your kids about what they're using the internet for and the information they are sharing."

The police urge those seeking further information about online safety to consult the website of NetSafe, at www.netsafe.org.nz.