SINGAPORE - The five-year-old was shy and withdrawn and often had nightmares when the Sngs first met her.
She was under the state's care, where children who were abused, neglected or unable to be cared for by their parents are looked after by foster parents or placed in a children's home.
It took about a year of regular visits - and doing different activities together - before the childless couple decided to adopt her in 2011.
Mrs Sng, a 67-year-old part-time pathologist, said of the first few months after the adoption: "We were prepared that these children may present challenges, and we didn't give up at the first sign of difficulties.
"She would cry and cry, and she was fearful of what would happen next. We had to calm her down, hug her and tell her that we love her and would never abandon her."
About a year after the adoption, the Ministry of Social and Family Development (MSF) asked the couple if they wanted to adopt the girl's biological sister, who is three years younger and also under the state's care.
Mrs Sng said: "Children are so precious and we were delighted. To be an only child can be lonely and we wanted to give her a companion."
The younger girl was more extroverted and adjusted to her new parents more easily, though they had to wean her from watching too many cartoons and too much screen time on the phone when she was first adopted.
The Sngs, who declined to give their full names, are among the few couples who adopt children placed under the state's care. In the past three years, the MSF has received fewer than 10 applications a year for the adoption of such children.
The couple were married in their early 40s.
Mr Sng, a retired information technology executive who is now 68, always wanted to have children.
When they were in their early 50s, they turned to Touch Adoption Services, which advised them to adopt an older child instead of a newborn infant, to narrow the age gap between them and their child, among other reasons.
The girls are now 13 and 16 years old, quarrel "like cat and dog", but love each other dearly, said Mrs Sng. The couple said their lives have been enriched by their daughters, whom they call a gift from God.
The couple took them to visit their birth parents a few times a year when they were first adopted, as they wanted to assure the biological parents their children were growing up well and for the girls to know their roots.
Mrs Sng: "But my elder daughter has asked to stop these visits as she wanted to move on with her life."
She said the support from professionals and other adoptive parents helped them to better handle the trauma and other issues their children faced because of their background.
Her husband added: "Be prepared to open your heart and love them unconditionally. They can feel it."