I'm in the "guide them" instead of "restrict them" camp, also due to restricting being pretty hard to accomplish baring moving to some remote Amish village. There is also no way I would consider a smart phone until high school, and any phone would be on a "need" basis, not "want". Some kids have them in 4th and 5th grade at my kid's school, it's ridiculous. Keep computers in family areas and get them in the mode of asking for permission for ANYTHING outside of what you've already approved and downloaded for them. So far.... seems to be working. I've told them to think of the internet as a massive public place, and just like they wouldn't be walking around a city without an adult, they won't be internetting without one either. I don't yet know what my high school plan is. Treat them like adults I guess if they earn it.
The only thing that stops a bad guy with a van is a good guy with a van