A unique email address is required for every user. This ensures that the session history is always valid and unique for that listener. One way to set up a unique email for a child that doesn't have one is to create an alias email. Each email provider has an option to create aliases.
Here is some information on creating an alias email from an existing Gmail account.
There are quite a few ways by which you can create multiple email addresses in Gmail.
For instance, if your email address is
email@example.com, any email that’s addressed to either
firstname.lastname@example.org will also be delivered to your main inbox since Gmail ignores dots and anything that’s after the plus symbol in email usernames.