In the last month, 200 more children have contacted Tinkle Friend, a helpline for primary school pupils, such that more staff had to be trained to help man it.
The children want to know if they will lose their friends whom they have not seen in weeks, and how to manage their online schoolwork. They also worry if their parents or they themselves will fall ill.
Anxiety due to Covid-19 is present even among young children, with Tinkle Friend getting more than 25 calls a day now, up from about 15 a day earlier this year.
The impact of the pandemic on children aged 12 and below can be serious, especially during the circuit breaker period, though many might be too young to fully articulate their emotions, said experts.
The Singapore Children's Society (SCS), which runs Tinkle Friend, said it received 564 calls and online chat requests last month, compared with 356 in March.
SCS director of student service Ang Hui Peng said it expects the spike to continue during the extension of the circuit breaker till June 1.
"Tinkle Friend is not a counselling service, but it aims to support children who are lonely and distressed and bring down their levels of anxiety," she added.
Children thrive on routine, which has been upended by the virus.
Child psychologist Penny Tok said younger children are apt to express their emotions through behaviour.
They become needier or act out, and can also experience changes in eating and sleeping patterns, such as eating more comfort food or having disrupted sleep.
"While younger children about three or four years old are more unaware of the situation, those six years and older are able to sense and react to the ambient tension from those around them," said Dr Tok.
Citing examples, she said one child whose father was out of work threw more tantrums because of the stress he felt emanating from his parents, though he did not understand the situation.
Another showed signs of obsessive compulsive behaviour such as hand washing.
Ms Ang said parents need to understand the emotions their children are experiencing. Rather than focus on punishing them for misbehaving, they can engage them on what they are feeling.
Children also model the behaviour of adults around them, so if parents are anxious, the children will also feel anxious, she added.
Dr Tok suggested that parents with young children could use storybooks with similar themes to encourage children to talk about their emotions, or use a drawing activity for an honest discussion.