The amount of time children spend using screens, such as televisions and computers, on a daily basis exceeds recommended guidelines but those guidelines were drawn up at a time when tablets, cell phones and other mobile devices were not as present in everyday life. Unless you are Amish or a doomsday prepper, it is unlikely that the future will mean current screen time guidelines.
And how valid are they anyway? Yes, prolonged use of screens by children is associated with adverse physical and mental health outcomes, such as increased risk of depression and anxiety in adolescent girls, but that is epidemiological curve fitting based on surveys, not real data.