In the European Union (including Italy) and probably in other countries of the continent, you must be at least 16 years old or be explicitly authorized by a parent or legal guardian to use the service. Instead, in the rest of the world, the age is 13 years. It is not yet clear how Facebook, a company that owns WhatsApp, will ensure that this part of the law.
In addition to sharing data between the various social networks of the Zuckerberg network (ie Facebook, WhatsApp and Instagram) there could be explicit requests for authorization to use which, once accepted, if not respected will be considered payable by the users and no longer payable by the society. This would allow Facebook to remove the legal problems that could derive from it by giving to users or parents the complete responsibility.