Children in third class and above have to wear masks in school from today onwards.
The government's also calling for less indoor socialising among under-12s for the next two weeks, after a sharp increase in Covid cases.
There were over 18,200 among under-18s in the fortnight to Sunday - compared to just over 13,700 in the previous two weeks.
Suzanne Connolly, the chief executive of Barnardos, is concerned about the new requirement for masks.
"It's really important that the impact on children's educational, social and emotional development needs to be monitored.
"Particularly young children - they really rely on social cues to learn how to relate to each other, and it's going to be far more difficult for children to communicate through a mask in schools, and to develop confidence in verbal communications."
