They are known as latchkey kids, or kids who are left alone at home.
Often it is because their parents are too busy. They would give them a set of the house keys and the children would return on their own after school.
But this creates problems, said Singapore Children's Society executive director Alfred Tan.
"There are many young children who come home to an empty house daily. Sadly, many parents are unaware that this can be dangerous."
He added that such cases usually involve low-income or single-parent families.
When left alone, children can get restless and eventually deviate from the routine set by their parents.
"They'd play with electrical sockets or fire. They might even climb the window to look out," said Mr Tan, who is in charge of more than 55 social workers, many of whom have encountered latchkey kids.
In their boredom, some might even leave the house without telling anyone.
Children under the age of nine are especially vulnerable because they are not mature enough to know the dangers.
Older children, too, can face problems if left to their own devices for long periods.
Persatuan Pemudi Islam Singapura Family Service Centre (East) centre manager Amran Jamil said latchkey kids are likely to be above seven years old.
Said Mr Amran: "Some parents perceive them as being able to care for themselves, at least for a period of time. As such, they may feel it is all right for their children to be left alone at home."
Older children may end up taking part in undesirable activities when their parents are not around, he added.
"For teenagers, there is the increased risk that they may engage in casual and pre-marital sex. Some may use the opportunity to spend their time playing video games or go on the Internet, surfing undesirable websites."
Child psychiatrist Brian Yeo said: "It's hard to tell at what age parents can safely leave their child at home. There's really no right answer."
He said while lower primary students under the age of nine are generally less mature, older children can also be inquisitive, leading them to trouble.
Said Dr Yeo, who is also a consultant psychiatrist at Mount Elizabeth Medical Centre: "It has nothing to do with the mental age of the child. It's not like young children are seeking to put themselves in danger.
"Kids are always curious, it's normal behaviour for them."
Dr Vivienne Ng, a psychologist in private practice, said the home environment matters for these kids, especially for those living in rental flats.
Said Dr Ng: "I have seen many cases of latchkey kids living in rental flats. These one- or two-room flats are not conducive for children as the environment can be unsafe.
"These children should not be left alone at all. There are childcare services and social workers who can help."