But the agent proved to be very persuasive, insisting that the director was almost certain to pick Wan-ki.

Sure enough, Wan-ki was duly cast. She completed filming within a day and the Wongs returned to their daily routine. Never in their wildest dreams did they think the advert for the Mannings pharmacy chain would be a hit or that Wan-ki would become a celebrity. Even now, two years after the ad first ran, his daughter still gets recognised wherever she goes.

'I didn't expect it to be so popular when more than 60 per cent of commercials feature children,' Wong says. 'Wan-ki enjoys the shooting and interviews most of the time and it's good that she got a taste of this field. She's now in primary two and learning about different types of occupations and she's proud of the fact that she's had some [work] experience.

'But it certainly brings us lots of trouble too. We are bombarded with invitations from the media and other companies, and our privacy is violated.'

Local child actors may not draw the kind of attention - or pay - that the young stars of the Harry Potter movie franchise did, but they face similar challenges. There's the matter of coping with public attention, for instance, and trying to balance work and study, issues that the youngsters' parents are keenly aware of.

Wong struggles to give Wan-ki an ordinary life. People recognise her wherever she goes and the constant staring makes his daughter - and any grown-ups with her - uncomfortable. For a while, she was pursued by paparazzi. Even now, strangers will approach and sometimes want to touch her.

'She gets frightened and runs back to us, which some will regard as being impolite,' Wong says. 'Many are well-meaning fans, but with all rumours of child kidnapping attempts going round, you just don't know if these people are just fond of Wan-ki or have a different agenda.

'I think Wan-ki is actually quite smart - that's what we taught her, to be careful with strangers,' he says.

In any case, celebrity isn't all it's cracked up to be.

'You can be happier being an ordinary person than becoming superman,' Wong says. 'People keep calling her the Mannings muimui [girl] and she doesn't like it. She says her name is Wong Wan-ki and she doesn't like 'Mannings' in her name.'

Her strong association with the retail chain doesn't seem to have put off other companies. Many still seek her out for advertising campaigns and Wong allows her to accept a few assignments as long as they don't conflict with their Christian faith or present an unhealthy image.

The pressure of homework has curtailed much of this work. Wong and his wife have had to reject many work offers, including movie roles, since she began primary school. But there's no denying Wan-ki is a born performer, he says.

'She's an active child who moves around a lot and loves imitating people, be it her teacher, us - her parents, or her grandparents; she's like Jim Chim Sui-man,' he says, referring to the stage actor and comedian. 'We're her audience and laugh a lot, while she enjoys it and finds it fun.'

Keeping his daughter's interests in mind, Wong has enrolled her in dance and swimming classes, but he aims to give her space to do as she pleases.

'It's her childhood, I want it to be a happy one rather than fill up her timetable [with classes],' Wong says.

Dr Mann Ka-fai, a psychologist and lecturer at the Open University, says being in show business can have a huge impact on a child's development. If not dealt with carefully, it can lead to big problems when they grow older.

'For children under 10, there are two things that are very important to their development: building their self-awareness and managing relationships with their peers,' Mann says. 'It's a time when they do not have to stick with their parents all the time and can develop on their own as social individuals.

'Children in showbiz generally have self-esteem constructed from external factors - their appearance or praise and attention from the public - which can be very negative,' he says. 'In the long run, that can make them too reliant on others to reinforce their self-image.

'But popularity may fade as fast as it comes and when that happens, they may break down and feel depressed.'

The parents of child actors Obe Tam Chun-yat and Suki Lam Chi-nok do their best to keep the youngsters grounded and make sure their education isn't neglected.

Now eight, Obe is already something of a showbiz veteran. He was cast in a TVB drama at the age of three and has since appeared in various commercials, more than 10 television dramas and two movies. His film debut, with Aaron Kwok Fu-shing in the 2009 production, Murderer, made him a widely recognisable face.

But while Obe enjoys attention, that doesn't mean he accepts the inconveniences it brings.

'Once he was spotted at a book fair despite hiding his face under a cap and people began following him around,' his mother Chow Man-lee says. 'It was chaotic and he became grumpy as he really wanted to play and have some fun, just like everyone else.'

However, Chow says her son isn't swollen-headed and manages to strike a balance between work and study despite a crowded schedule.

'It wasn't a problem at all when he was in kindergarten,' she says. 'But in primary school, the amount of homework grew, with 10 to 12 assignments each day. However, he has been quite efficient and is able to finish them during free time between filming or dinner breaks.'

Chan Mui-ying also reckons her daughter, Suki, is coping well.

'Suki is having tests this week, but she's still going for a shoot tomorrow night,' Chan says. 'To me, study is about progressive accumulation of knowledge. So if she works hard enough on a regular basis, it wouldn't be a problem. Her academic results are pretty stable.'

Suki made her debut in a baby commercial and has appeared in many television programmes. But it was only this year - with her role in L'Escargot, a TVB serial built around Hong Kong's property bubble - that she began to draw wide attention.

Chan was surprised by how much her daughter's televised scenes could tug at heartstrings even though she had been present throughout the filming.

'She did quite well, especially in sentimental scenes,' Chan says. 'She didn't take any acting lessons. It was all her effort and communication with the director.'

Since then, people would greet Suki on the street, grown-ups gave her lai see packets during the Lunar New Year, and fans, including one university student from the mainland, sent gifts.

But Chan says she reminds her daughter often to be grateful for the opportunities and see them as incentives to improve herself. And she has impressed on Suki that she must work hard at her studies if she wants to take on new acting roles.

The children have gained more than recognition, pay cheques and good communication skills from their acting forays, their mothers say. Suki's mum, for one, is proud that her daughter has learned to be independent and responsible. Similarly, Chow reckons her son's horizons are broader than many other youngsters his age because he has seen more and experienced more than they have.

Still, growing up in show business brings a special set of problems. 'The children deal with adults a lot, so they incorporate adult values and problem-solving skills straight away,' Mann says. 'Many child actors can become too mature, reflecting the fact that they are not learning to cope with stress and conflict from their peers and don't have a comprehensive social environment.

'They may not be able to find people their age to talk to, some may vent their frustrations through negative habits, such as drugs, when they grow older.'

Fleeting fame and the commercial imperative in entertainment circles can also affect the children's psyche, Mann says, and parents should encourage more interaction with other youngsters so that they don't become egocentric.

Obe is already encountering some of these bumps, cushioned somewhat by his mother's efforts to keep him down to earth.

'He is rather worldly for his age and can be too money-minded' although he is often careless with spending,' Chow says. 'He started working early and money has come a little too easy for him.

'Sometimes, when he sees an item he wants, he would say, 'Oh, it's very cheap'. I always tell him that even if he has money in his bank account - we've saved the earnings for him and he knows exactly how much he's got - we have to assess the value of an item. Every dollar counts, so we should compare prices at different supermarkets, for instance. Why should we pay more for the same product?'

And at the ripe old age of eight, Obe is also in the midst of a midlife crisis.

'Obe became unhappy as he didn't receive as many job offers as he used to,' Chow says. 'He would ask me if that was because he has grown older or gained weight. I explain to him that the career of a child actor is very short.'

Despite the uncertainty, the parents remain open to their children pursuing acting careers when they grow up - as long as they finish their studies.

'If it is what she wishes, I won't object,' Wong says. 'But I would rather she grow up to be a decent person than be high-achieving but arrogant. Being famous at this time means nothing.'