On the inactive list there seems to be no difference between a new member waiting for their COPPA letter and a new member waiting for a reply to the "welcome" email.
The Email Admins receive for activation does not mention COPPA.
The table of inactive users on the ACP home page shows "Newly registered Account" regardless of COPPA or not.
Only if you go to
ACP >> Manage groups > Registered COPPA users >> Members
do you see that the inactive new member is COPPA and can guess that you have not received the parent letter yet. I do not see any other way to differentiate between COPPA users and other reason a newly registered user's account is inactive.