You can create a MAUVE ID by creating an RSCA account, you can do this HERE.
I CAN'T CREATE A RSCA PROFILE FOR MY CHILD/PERSON WITHOUT AN EMAIL ADDRESS
If your child does not have an email address yet, you can take the following steps to create an RSCA profile
Go to account.rsca.be > register > fill in your email address + name of the child (for example: [email protected]) together with a password of your choice. Then fill in the rest of the child's information.
After creating the profile a verification email will be sent to your email address. After clicking "Activate email address" the child's profile is created and you have a Mauve ID for the child that you can enter during the ticket purchase.