I think the key is that at a young age, they lack the self-control needed to know when to pull themselves away from the screens. They need to be reminded to go

I think the key is that at a young age, they lack the self-control needed to know when to pull themselves away from the screens. They need to be reminded to go to the bathroom, eat meals, go to sleep, etc. By not being proactive with limiting the time, you risk delaying them learning the basic self-control. The good news is they gain these skills over time. I can see my 4 year old already gaining this control which she lacked earlier. The thing is it takes some diligence from the parents until they get there.