impact of modern technology on children's ability to learn at school.
The Association of Teacher and Lecturers (ATL) is concerned at how long children spend on computers and digital gadgets outside school.
It said some pupils were unable to concentrate or socialise properly.
The impact of digital technology is the focus of the union's annual regional conference in Belfast on Thursday.
Mark Langhammer of the ATL said: "We're hearing reports of very young children who are arriving into school quite unable to concentrate or to socialise properly because they're spending so much time on digital games or social media.
"We'd like the Department of Education to issue guidance to all parents on the maximum amount of time which young children should spend on these devices, and on how kids can use digital technology safely and sensibly."