let them use PC and mobile

[inovacije]

I'm a software engineer. And I spend a lot of time on both my PC and mobile.

Shall I let my kid use any of them, or not?

I'd say yes. But give clear rules on how long they can use it, for what purpose it is, and stick to it.
They must learn that these devices are not just play (even though we use them for play), and that they are part of our everyday's life, much like TV 40-50 years ago, or a plow 300 or 400 years back.