It should, but what does the law say?
In Greece for example, it is illegal to serve baby seafood of many species, following the over-fishing in the Mediterranean.
So, is it illegal in Italy to serve baby seafood?

It should, but what does the law say?
In Greece for example, it is illegal to serve baby seafood of many species, following the over-fishing in the Mediterranean.
So, is it illegal in Italy to serve baby seafood?

No it is not illegal.
Octopus are not subject to EU quotas and there is no minimum landing size. https://www.mcsuk.org/goodfishguide/search?name=Octopus,%20Lesser
It is not unusual in Italy to eat baby octopus.