In order to view your subaccounts, first login to Twilio.
When you login, you will be in your main account (also called the "master" account) by default. You can switch to your subaccounts by clicking on the down arrow next to your name, at the upper right hand box.
Clicking on subaccounts will take you to a page where all your subaccounts are listed. Closing a subaccount will make it disappear from this list.
How do I get back to my master account?
When you choose to "View Subaccount", an orange header will let you know the information you are viewing is for that subaccount. To return to your "master" account, you would click on the "Switch to Master Account" link in the header.
Your subaccounts are also accessible through this link.