To set up a parent account with Tynker, go to tynker.com and click "Join For Free" in the top right. You will be prompted to enter your e-mail which will be your username for your Tynker account.
You can sign up using Google, Microsoft, or Facebook. If you use one of these options, you will need to always use that option to log in again. Resetting your password through Tynker will not work, you will need to go through either Google, Microsoft, or Facebook if you forget your e-mail.