Andrea Yee was initially fearful of telling her daughter she was adopted.

The former marketing professional who is now a full-time mum said: "At one point, we thought of burying the truth. I was insecure and worried about losing my daughter."

But she knew she had to deal with her fears after hearing horror stories of children who react badly after learning the truth by accident.

Madam Yee, 42, joined a support group for adoptive parents and now shares her experience at workshops to educate parents about the importance of telling children the truth and how to do so.

She has also written a book, We Just Want You To Know, to help parents break the news to their children.

The workshops are run by charities like Touch Adoption Services, which is part of Touch Community Services, and Fei Yue Community Services.

Touch started the workshops about a decade ago after some parents asked for help. They had hidden the truth and their children became depressed on discovering by accident that they were adopted.

Other children began rebelling against their adoptive parents, said Touch senior manager Teo Seok Bee.

Fei Yue senior social worker Cheng Wen Shan said: "The impact on the child can be devastating when he learns the truth accidentally.

It affects his sense of identity, security and trust. If you don't tell the children why they were adopted, they will imagine the worst."

Experts say adoptive parents should be the ones to first tell a child he is adopted, and this should be an ongoing process as the child grows up. This way, they strengthen the parent-child bond and can help the child deal with questions and feelings of loss and sadness, said Ms Teo.

Madam Cheng said parents should tell as early as possible, when the child is as young as three, and can raise the matter by reading children's stories on the topic.

"Adoption is not something shameful or something to hide," she said. "If we don't talk about it, it becomes more taboo. I feel parents are more open and more willing to tell the truth now as they are more educated and want to do what is good for the child."

Madam Yee, who is married to a 45-year-old human resources manager, started telling their daughter about adoption when she was two.

She took the girl to visit a friend who had also adopted a baby to explain the idea.

At first, the girl had no clue what adoption meant. Once, after learning that some animals lay eggs while others give birth, she asked:

"Mummy, did you give birth to me live?"

Madam Yee recalled: "I said, 'No, your tummy mummy gave birth to you.' Her next question was, 'How about ducks?'"

The girl was three when, on Mother's Day, she asked for her "tummy mummy".

Madam Yee told her she had prayed for the birth mother's well-being, but she and her husband have no contact with the young Singaporean, who was an unmarried teenager when she had the baby.

Their daughter is now eight. The couple have a second adopted girl, born to another Singaporean unwed mum in her 20s.

When the younger girl, now three, asked Madam Yee recently if she gave birth to her, the older one jumped in to explain: "Mei Mei (sister), you came from your tummy mummy. Mummy can't have any babies so we have two mummies and two daddies."

Madam Yee said: "My elder daughter has embraced the fact that she is from an adoptive family."

But the girl is also curious about her birth mother and has asked what she looks like, if they can meet, and if Madam Yee would be jealous if she called her birth mother Mummy too.

Last year, she asked for her birth mother's name, went online and found a Facebook member with the same name. She did not pursue it further.

Madam Yee said: "I want to respect her desire to look for her birth mother but it has to be when she's older and emotionally ready. But I don't know if her birth mother will be ready to meet her."