both of the answers above are incorrect
The Childrens Online Privacy Protection ActCOPPA'd users are those who have certain restrictions applied if we know them to be under 13 and residents of the USA. Because of the COPPA law of the US, they cannot send trade messages, PMs, set up avatars or signatures, or post in the forums. The only exception is for posts in the oekaki board, where all their posts must be pre-approved by staff before they show up in the forum. If we discover an American user to be under 13 then we will apply the COPPA protection, at which point all of the above restrictions immediately apply.
COPPA users can remove their protection before turning 13 if they send in a signed parents permission form. If they don't send in a form, the COPPA protection will be removed when we know they have turned 13 (i.e. if we have their birthdate on record, and observe their 13th birthday)