The only secure method is whitelisting (domains and IPs). It's an absolute pain the assets, however.
I would go with good adblockers and a domain-tool like Pihole or similar. They usually have some decent block lists that will catch 90% of accidental attempts to visit bad places, and blocking ads cuts out 99% of the temptations there anyway.
Put the computer(s) in a public place in the house, make sure they have a decently sized screen so parents walking by can see what's going on.
Make sure the kids know they will never get in major trouble by telling you what is happening, and no trouble at all if someone (online) told them not to tell you - those are big red flags.
I would go with good adblockers and a domain-tool like Pihole or similar. They usually have some decent block lists that will catch 90% of accidental attempts to visit bad places, and blocking ads cuts out 99% of the temptations there anyway.
Put the computer(s) in a public place in the house, make sure they have a decently sized screen so parents walking by can see what's going on.
Make sure the kids know they will never get in major trouble by telling you what is happening, and no trouble at all if someone (online) told them not to tell you - those are big red flags.