A small Golden Bay primary school has restricted cellphone use at school after a seven-year-old pupil showed others a South Park video with sexual themes.

Motupipi primary school principal Mark Cullen said the incident involved a child who brought an older sibling's cellphone to school and "showed some children an inappropriate clip that had been downloaded from the internet".

"All parties involved were promptly contacted and the issue discussed."

The cartoon images from the popular TV series South Park, showed sexual images involving poking and prodding in sexual areas. Some of the students who were shown the images were disturbed enough to report the matter to the school authorities.

The Motupipi school board of trustees discussed the incident at their meeting last month and decided to actively discourage cellphones in school.

"We are aware that cellphones are very useful and an important part of our lives now, however, we also feel that currently they are not necessary for our children to have at school," Mr Cullen said.

"Cellphones are very portable and have the ability to quickly access content that may be inappropriate for the age of our children and the reality is that we can't check the content of phones."

Students at Motupipi will be asked to hand in their phones at the office at the start of the school day and they will be returned when school is finished. No student will be allowed to keep cellphones, MP3 players or similar devices in their bags or on their persons during the school day.

Students breaking the rule will have their devices confiscated.

Mr Cullen said the school's board planned to draft a comprehensive policy with clear guidelines on the use of information and communication technology.

"The aim of this policy will be to promote and ensure the welfare and safety of children and young people when using the internet and to prevent children from being exposed to inappropriate material."

Sean Lyons, chief technology officer at Netsafe, said many schools were facing similar challenges on a daily basis. A number had imposed restrictions on cellphone use.

Mr Lyons said a Waikato school had experienced incidents involving cellphones and decided to raise the issue with their community.

"They spoke at length to their community and they got the support of the community in the decision to ban the use of cellphones. They seem to be experiencing some very real success with that."

Mr Lyons and Netsafe experts provide free support and resources to schools. The Ministry of Education funds Netsafe in an effort to educate teachers, schools and students about the complex issues surrounding technology, education and cyber safety.