As a parent you can create Google or Microsoft accounts that you control for your children.
If you have a Google account, the easiest way to create an account (email and password) for your child is to download the app Google Family Link (available on Android and iOS). In the app, sign in with you Google account and create accounts for your children.
If you have a Microsoft account (e.g. Hotmail, Live, Outlook), you can download the app Microsoft Family Safety (available on Android and iOS) and do the same as for Google Family Link.
Then your children can sign into Clixzy using the new accounts.