A growing number of parents are sending private investigators to check whether their children have gone astray, sometimes even overseas.
Eight out of 10 private eye agencies contacted by The Straits Times said they have seen a rise in such cases.
Mr David Ng, 37, director of private investigation firm DP Quest, said his company has seen a 20 per cent year-on-year increase in such requests.
"Parents get worried when they see changes in their children's behaviour - for example, if they get a tattoo, or start staying out late," he said, explaining the reasons his clients usually cite.
The children are usually in their teens, in secondary school or polytechnic.
Private eyes usually follow their subjects for three to five days to glean a pattern. Often, the parents' suspicions are proven right.
Their children have been discovered to be involved in illegal activities like drugs or gambling.
Other times, they are also found at Internet gaming shops late at night without their parents' knowledge.
Video or photographic evidence is then presented to the parents, who decide what to do next.
Such services do not come cheap. Three days of tracking, which is usually sufficient, may cost about $3,000.
Private investigators said they start tailing the children as early as when they go to school in the morning.
Mr Joe Koh, 41, from Justice Investigations, who has been a private investigator for 13 years, and sees one or two such cases a month, said that usually both parents are working and too busy to monitor their children.
He encountered a case where a Secondary 1 student would bring friends home in the day to sniff glue, then leave to hang out with friends till late into the night.
Investigators like Mr Koh face challenges such as staying undetected for long periods and tracking children at secluded spots.