They are among an estimated 40 million children worldwide who have missed out on crucial early education due to the pandemic.

UNICEF recently looked at the state of pre-school education, and the impact of COVID-19 closures and disruptions has been massive.

"Education disruptions caused by the COVID-19 pandemic are preventing children from getting their education off to the best possible start," Henrietta Fore, UNICEF's executive director, said in a press release. "Childcare and early childhood education built a foundation upon which every aspect of children's development relies. The pandemic is putting that foundation under serious threat."

Here in Vietnam, about 4.4 million preschool-age children have seen their learning disrupted. A survey conducted by the Vietnam National Institute of Education Sciences found that 41% of school administrators and preschool teachers from around the country said parents are worried about the pandemic's effect on their children's education.

Other research has reportedly found concerning drops in the number of meals and the quality of nutritional intake among young children in recent months. Lower income groups have particularly struggled.

"In Vietnam, during school closure period, efforts have been made to provide pre-school children with online learning opportunities. However, a lack of internet access and devices, limited digital skills of parents and the fact that preschool teachers are largely unfamiliar with new technologies made it challenging to facilitate learning through play online. This brought an extra burden to families of young children," Simone Vis, chief of education for UNICEF Vietnam, was quoted as saying.

Children stuck at home are also at greater risk of abuse from family members, while a lack of social interaction can hinder development.