If you are an ABN Amro customer, you need to remove the bank connection to the ABN Amro account in order to delete a user account.
How to delete a child user account:
Go to "Settings" in your parent user account
Click on "Connect child's bank account"
Click on the red trash can symbol next to the account you want to delete
Now your child can delete his or her user account in their Gimi app
How to delete a parent user account:
Go to "Settings" in your parent user account
Click on "Connect child's bank account"
Click on the red trash can symbol next to all connected children's account
Go back to "Settings", at the bottom of the page you can delete your user account