The chief executive of Childnet International - a charity that is a member of Facebook's Safety Advisory Board - said he thought the firm had more work to do to communicate the change.
If they don't get permission, teems will get a generic version of Facebook that's not customised for them.
If you're using WhatsApp in Europe, you may find yourself needing to verify your age or the age of a minor in the coming weeks.
Facebook and Twitter, along with many other organizations, have started the process of making changes to their privacy policies in order to conform with the new regulations and to make it simpler for the users to understand how their data is utilized.
"Our goal is simply to explain how we use and protect the limited information we have about you", Facebook said about the new WhatsApp regulation.
Facebook unveils appeal process for when it removes posts
There'll be a link to request a review, which will be carried out by a person, and "typically within 24 hours", Facebook promises. Facebook has recently been grappling with backlash for how it handled the data breach scandal involving Cambridge Analytica.
Facebook, which has also been criticised for its handling of personal data, is taking a different approach to younger users on its main service.
Moreover, the minimum age required for a WhatsApp users will remain 13 years in rest of the world in-line with its parent company.
European Union was chiefly concerned over WhatsApp's sharing of user data with Facebook, its parent company.
Ahead of GDPR, there is a clear trend toward greater control over how and when children access digital platforms, most likely a reaction to the concern about data privacy issues by parents and regulators.
The rules give Europeans more control over their personal data.