It's hard to generalize too much about screen time. It is almost universally bad, especially for kids, and should be kept to a minimum. Gadgets nowadays provide an unlimited stream of stimulation, novelty, and dopamine hits. No child can resist that, which is why the "lesser evils" like education apps are still "gamified" to have any chance of keeping a kid's attention. The result is that kids from an early age are growing up addicted to dopamine and the internet. It's not much different from fat kids already being addicted to junk food from an early age, it's just not as visible -- and both situations will be very difficult to change during the individual's life.
Really, you just have to spend some time with the current generation of children to see how disastrous technology has been. Their brain chemistry depends on constant outside stimulation, and anything else is boring.
Also, if you think you can effectively police what your kids do and see on the internet, you are sorely mistaken.