Question

How can parents protect their children and let them explore

Answer 1

with blocks on bad websites

Answer 2

mor explainatory

Answer 3

The parents could have an administrator account and block certain types of websites for the childs account like they could block anything that contains nudity, violence, and social media sites.

Answer 4

Parents can watch over what their kids do, just not try to totally control their kid's life. I agree with @989freak but you also have to consider that there is a lot more to protecting children than watching their internet activity