I think this is where web of trust comes in. You could create some sensible defaults to keep garbage out and then delegate people you trust to help you filter stuff out. 

That doesn’t mean kids won’t see everything they don’t like and I’m not sure if there’s a fix for this. You’ll always see things you don’t like until you mute them. 

 You can never really solve DM harassment if you can’t stop yourself from reading the text - that’ll always be the responsibility of the person involved