I have two kids, a 5 year old and an 8 year old. We introduced the ipad and similar technology to my son at age 3, and my daughter at about the same age. My son also plays video games on the PS4.
My view is that in this day and age, insulating kids from technology completely is not feasible. My wife and I have therefore tired very hard to teach our kids how to use and enjoy technology responsibly. For the most part, that means teaching our kids when it is ok to use technology and when it is not, and, to a great extent, limiting how much "screen time" our kids get. At present our kids get about 1/2 an hour of screen time a day during the week, and that is right before bedtime (7:30 - 8PM). There are some exceptions, such as when my son was researching a topic for school (in which case we let him use the ipad to look up facts about his chosen topic with adult supervision). On the weekends, the kids usually get about 90 minutes of screen time a day. An hour in the morning (before mom and dad wake up), and the same 1/2 hour before bed. We do give some leeway for my son as well when he is using the ipad/iphone to further learning. For example, he plays a lot of math games on the ipad - and when he is doing that it is hard for us to tell him to quit. Particularly as he already has a solid foundation in math topics that are taught in 4th and 5th grade (he is in second). It is similarly difficult to tell him to stop reading when he sneaks a flashlight under his covers at bedtime and is caught reading hours after he was supposed to go to bed.
Interestingly, the hardest part about teaching our kids how to appropriately use technology has been preventing ourselves from inappropriately using it in front of them. My wife and I are both professionals and we both have smart phones with work email, etc. on it, and clients that expect us to respond quickly. So it is very difficult not to have the phone sitting there at dinner, or always in my pocket, etc. And its even more difficult not to answer when said phone rings, beeps, or otherwise triggers the pavlovian response.