Then they'll have great survival skills.
Or... you know... not.
Are there risks? Sure. But there are risks in everything. And, by the way, that phone can distract your kid while crossing the road, ending up in a much more likely dangerous situation.
Plus, the idea is not about banning phones altogether but rather regulating them, using them wisely. You know, like how we should use literally any tool ever invented? Having an appropriate usage based on age and situation is called responsible parenting, not Orwellian control.
We can either raise a generation of mindless zombies glued to screens, or we can try and foster responsible and thoughtful use of technology. I know which one I'd prefer.
Let's give them guns too, because what if a giant bear comes in that cliff?
When I was a kid, I got to play with the cast-off computers my dad would bring home from work. If he had your attitude, he would have thought, "oh, we didn't have computers when I was a kid, so certainly there's no value in my son having one".
The difference? Well, the key was that I had just some time slots I was authorized to play in a week and I suppose responsible parents now do the same with their kids smartphones.