Different clients have different filter mechanisms, you also should only see what you follow, except you get it pushed somehow in the suggested tab. You yourself could create nostr client that focus on filtering or even reporting those things, or creating a safe space for kids (like youtube for kids, nostr for kids). Overall it needs ideas (you could also have AI filter stuff and you train it what gets filtered and what not).

At the end, it needs a lot of brain and good ideas to solve this problem. The beauty in nostr is, that it is decentralized and uncensored.