@wessburt if clicking My Account takes you to the homepage, you've logged in with the wrong username. It's possible to have multiple Sky iDs and only the one attached to NOW TV will work. If you've had Sky Broadband or TV in the past your browser may have auto completed your old username. Try other usernames you might use or the forgotten username link on the login screen.
Also you could look through your emails for communications you've had with NOW TV and see if any of these include the correct one, or load the app which you've been watching on and check the settings to see which username is on that.
Once you've got the right one, clicking My Account will show the passes and you can cancel them with a few clicks.
Thanks for your post.
It can be possible that your grandchildren may have accidentally purchased the pass. To make sure these surprise charges don't happen, we advise our customers to set up Payment PIN that will only be known by the account holder.
I'll look into this for you and contact you via email. Please keep an eye on your inbox.
NOW TV Team