I don't see that many kids using the #fediverse right now, even for something like pixelfed, or loops, or peertube.
Big instances on fediverse look like "small social network" in the EU categorization.
Maybe the rules will apply just to "big" commercial operators.
But let's say all those people from X and IG and TikTok and Youtube all came to mastodon and mastodon became the great thing in Europe.
If they will start to ask for age verification there, people will start using something like #holos where everyone is doing self hosting just from their phone/app.
Age verification became then the bare possibility to own a phone and a sim card, it should have always be like that.