The Association of Teachers and Lecturers (ATL) said it has received an increased number of reports from teachers worried about the impact of overuse of digital technology.It warned that children are arriving for lessons unable to concentrate properly because they are spending too much time on games or social media.The union is calling on the Education Minister to take action.Mark Langhammer, NI director for ATL, said: "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."The union said there is currently no official guidance for parents in Northern Ireland on how much screen-time is safe for their children, or on how early children can be introduced to digital devices.However it added that guidance issued by the American Academy of Paediatrics in the US indicates that children and teens shouldn't be allowed more than one or two hours per day.Emma Quinn, who teaches a mixed P4 and P5 at a Newtownabbey primary school, said many children lacked motivation and found it hard to focus on anything which was not exciting."There's a complete lack of motivation among many of my pupils - these gadgets are really destroying their ability to learn," she explained."They're so used to the instant buzz which you can get with these games and gadgets that they find it really hard to focus on anything which isn't exciting."All they want to do is to get back home so they can play on their Xbox or get on their tablet again."