Both books are surprisingly gentle in tone, but unflinching when it comes to the emotional hardships of Cambodia's so-called "Year Zero".

"Working in the refugee camps made me want to write about them later," says Ho, who is visiting Hong Kong to give talks at the Young Readers Festival, which starts next week. As part of the schools programme, she will discuss how her experience in different cultures has influenced her writing.

"I felt that there were some things that I had not really addressed while working in [the camps]," she says. "The refugees were clinging to their lives just trying to survive in the camps. If you were an aid worker, you were busy helping them to survive.

"There wasn't a lot of time for angst and introspection. While I was working there, it was natural not to look at what was going on objectively.

"I was totally wrapped up in the day - how much soup to cook, how much rice to buy. But afterwards, I felt there was something that I had not directly looked at, grappled with, or listened to. The books were a result of that."

Ho's route to the refugee camps was itself an adventure. She was born in 1951 in Burma to Chinese immigrants (her father, Ho Rih Hwa, was a prominent Singaporean entrepreneur and diplomat who headed the Wah Chang group, now run by her brother Ho Kwon Ping; her mother was Hunan-born writer Li Lienfung).

In the 1950s, business interests took the family to Thailand, where Ho went to school. In an appendix to , she says that her early life in Thailand was probably very similar to that of children in Cambodia at the time, although she never visited the country.

She left Thailand in 1970 for the United States, where she studied at Cornell University, before returning four years later to teach in Chiang Mai. The Khmer Rouge took power in Cambodia in 1975, and launched a programme of genocide on its own people that claimed about 2.5 million lives. Ho says that at that time most Thais were unaware of the atrocities that were being committed over the border, which the Khmer Rouge had sealed.

"I was only a few hundred miles away. Yet all that time I knew little of the nightmare that Cambodia had been plunged into. Nobody knew," she writes.

When the Vietnamese army invaded Cambodia in 1979 - in retaliation for border attacks by the Khmer Rouge - word about the horrors finally spread. Appalled, Ho enlisted to work with a refugee agency at Nong Chang in 1980. (The camp was also home to about 100 Cambodian guerillas, which meant that it was a frequent target for Vietnamese shelling.)

Working as a nutritionist, Ho saw many malnourished children. But it was the healthy ones that stuck in her memory and later inspired her to write, she says. Consequently, her books are peopled with tough children like Dara, the resilient and resourceful heroine of .

"The stories of the children that I saw were never told," she says. "Journalists would interview the refugees, but generally just the grown-ups. But I used to like watching the kids, and I always wished that I had time to understand them better, to get to know them, to befriend them.

"I looked like them, and given just a tiny tweak of circumstances, I would have been one of them, so I would have played with them and suffered as one of them. I really admired their gutsiness. There was something wrong with the status that they were accorded - because they were not helpless victims. These children were actually the survivors. They were gutsy."

A singular exchange with a child in the camp has stayed with Ho to this day.

"One of the few moments [in which] I had a direct impact on, and exchange with, a [child] was when I was peeling a tangerine for lunch," she says.

"A little girl watched me peeling it. She didn't beg at all, she just watched me intently. So I gave her the tangerine. But then I was surprised - because she gave me something back.

"She didn't just take the tangerine and run. She gave me a clay marble that she had been rolling out of mud. I really thought about that clay marble a lot. It's like the grit of sand in an oyster - it makes you uncomfortable, so you put things around it to make it smoother. I think I formed the story of around that one event."

Although the books deal with frightening moments like air attacks, and record a startling number of deaths, the prose is lyrical rather than shocking.

Terrible events are often related in a very matter-of-fact way by the child protagonists, whose will to survive takes precedence over their fear and loss.

"I haven't seen or experienced any kind of violence first-hand," says Ho.

"It would be gratuitous for me to describe it without seeing it myself. The darkness in my work is usually the aftermath of the violence. I have been in the refugee camps and I have seen the children starving, the amputated limbs. But I have not seen people fighting each other."

Ho now lives in Ithaca, in New York state. She moved to the US after marrying international development consultant John Dennis, who she met at Cornell. They have three children: Danfung (a photojournalist whose documentary on a US marine's experience in Afghanistan, was nominated for an Oscar last year), Mary Xiaofeng (whom the family calls Mei-mei) and Christopher.

Ho has written numerous other young adult books focusing on Southeast Asia, including , which is dedicated to the 46 students killed by Thai soldiers at Thammasat University in 1976. She has also written books for young children, including , a Thai lullaby that she composed, and , a translation of Tang dynasty poems for children.

"When the children started arriving, I had less time to write," she says. "My husband was studying for his PhD. So I only had the children's nap times to do anything of my own. I just had little bits of time to write in, so I wrote the children's books."

Ho remembered that her mother had taught her Tang dynasty poems as a child, and was an attempt to foster her own children's interest in Chinese culture.

" was intended to be a cultural bridge from my children to their Chinese grandmother," she says.

"But when my mother died a year and a half ago, I realised that the poems were more likely to be a bridge between me and my mother than my children and her. I can form a picture of her from the poems that she had spent so long teaching me - which I tried less successfully to teach my own children."