I think that online exposition should be managed through each age by choosing the appropriate device/online filtering:
1st stage - offline tablet with selected apps.
2nd - laptop with internet content filter in a separate device (e.g. router openwrt with adguard).
3rd - Smartphone with parenting control
But the most important part is education. This is just as using that helping wheels when learning how to ride a bicycle, you need to ensure that your children is ready when you take off the safety, so they don't fall.