There could be whitelists of accounts with child friendly contents.

If a site wants to only post child friendly content it could apply for whitelists.

There could be Clients with the ability to only display whitelistet contents and the parents could manage wich whitelists they prove and also manage an own whitelist.

Everyone should be able to create whitelists but also everyone can chose which whitelists he/she wants to use.

Also there should be nested whitelists so somebody can add whitelists to his/her whitelist.

I think with this modifications nostr would be better for kids than facebook/twitter etc. and there would be no problems for adults with this modifications and nobody is forced to use whitelists.