Obviously, I know its impossible to completely child-proof a PC, but theoretically, what steps would you take? Assume its a laptop with internet access, meaning you'd want local solutions and something like a pi-hole wouldn't work well.
I would personally assume, you'd want to:
A) discourage internet exploration by offering ready-to-use options for most needs, such as thumbnails/bookmarks for common websites.
B) Implement some sort of blacklist for common or easy-to-stumble-upon negative content. Maybe something as simple as a Ublock filter?
C) Robust monitoring tools, although I have no idea what.
Edit: To be clear, I know education is the number one tool, but let's say a tech illiterate friend is asking for help. What might you set up for them, or recommend they use - tools to assist in parenting, not replace it.
I disagree that pihole can't be used in the instance of a laptop since you can still use it as a dns remotely, but an opendns account was effectively made for this purpose.
Use commonly available white lists and blacklists for kids only content.
Pihole also has built in monitoring for dns requests. I've never paid for opendns but it does too.
Arris routers allow smtp data logs to also show direct IP interactions. I imagine lots of routers do. Using solarwinds software demos you can easily parse through them. You cannot control these requests non-locally, but I'd ask what you're trying to look for if these requests are consistently made out of the house and are limited to IP only requests without dns. An app you don't want them using? In that case reroute the apps known IPs to 127.0.0.1 locally and remove admin rights from the user. This will also lock them to opendns.
Set rules for yourself about what constitutes a problem ahead of time. Snooping can lead to the bending of rules in search of something that's not there. Internet traffic is rife with advertisers sideloading all sorts of dubious shit. The context of other IPs or hostnames connected to before and after is important when looking at log data.
Edit: Easiest way around this is to install a USB nic. A domain and GPO is how corporations prevent this scenario with minimal user impact.