Both parents and the child who has reached the age of majority must notify the CPC separately:

• The parents must each request the removal of the child’s foreign account from their own list of foreign accounts. The easiest way to do so is through the online application ("closure/decumulation" option). This can also be done by filling in the closure/decumulation form in hard copy.
• The adult child must notify the CPC, separately from his or her parents, that (s)he is now the holder or co-holder of a foreign account. This can be done through the online application ("add an account") or using the paper form for the reporting of foreign accounts. 

A hypothetical example of such a notification can be found here.