Does each account need a unique email address?

Solution 1:

Your account as an adult should be the main account, under which you can create sub-accounts for children. This will require only one email address.

The process is outlined in Sony's Playstation 4 User Guide.

To summarize, to create sub accounts, this is the process:

Select [Parental Controls] > [Sub Account Management] > [Create New Sub Account], and then follow the screens to create a new sub account.

You can also set parental controls there.