The research does not support this view. It is ironic that it is often the same people who charge that today's kids are becoming glued to the screen that also say they have lost their attention span. A more thoughtful view comes from demographer Eric Miller.
Kids hate to be bored.
They have shorter attention spans, are used to a diet of highly stimulating visual information. From an early age they are gratified instantly and so have less patience for delay of any kind. True, they are used to a Stimulating environment. True also, kids hate to be bored. This is not surprising, given that they are more knowledgeable, likely smarter and more active than their boomer parents.