A child you can have that conversation with is when they’re in school and exposed to using computers both for leisure and for work. If they’re like 6 and under then they shouldn’t be using screens in the first place or if they do its under direct supervision.

I’m not confident that parental control software is a solution to something thats ultimately a behavioral/self control issue and a societal one as well. Adults also deal with screen overuse.

Obviously you can still implement things like locking app installation behind your password or setting up a DNS level blocker on your home router (both of which can be done for the sake of safety online) but I don’t think setting up control software is the best approach to take since the child is going to find out you’ve been limiting them once they see their peers who dont have parental control software placed on them.