To create a tournament, you must do it from your club.
If you still don't have a club, make sure to follow these steps using your adult account:
How to create a Club
Click Manage from the menu on the top and select Clubs:
Click on Create a Club under the Clubs menu on the right side of the screen:
Fill out your club information and click Create at the bottom of the screen:
Create a Club Tournament
Now that your club is created, go to Play in the menu at the top and select Play vs Kid:
Click New Club Tournament:
This will bring out a pop-up window where you can customize your Tournament. Don't forget to click Create to bring your Tournament to life!