Rosmah Mansor has urged parents to be more stern with their children following an accident in Johor, which killed eight teenage cyclists and wounded eight others, in the wee hours of Saturday morning.

The wife of Prime Minister Najib Abdul Razak also told parents to keep tabs on their children's whereabouts.

"I feel so sad over the incident. I hope parents will give their full attention to their children.

"If they (the children) go out, parents must know who their children are with, what are they doing and what time they should return home.

"Parents must be strict," she told reporters after the launch of a seminar on sexual crimes against children in Putrajaya this morning.

Rosmah expressed concern over the increasing number of sexual abuse cases involving children.

"I didn't know that this is widespread... When I received a briefing (from researchers), I was shocked that the statistics is increasing and how much planning is involved by those involved in child sexual abuse.

"I felt compelled to educate the public on the severity of the matter... If we don't inform parents, this will spread," said Rosmah, who is the seminar patron.

She urged parents to monitor their children's activities, particularly their mobile phone use.