Assigning child records to a new record

Hi

I am designing a soluton for transfering child records on contact/account to new records. The scenario is this:

A contact can be converted to an account, and an account can be converted to a contact. In the first scenario the data warehouse  creates a new account and deactivated the old contact. But how do we transfer the activities, opportunities and cases from the contact to the account in an automated process? Is this achivable with the use of a workflow?

Thanks for help and tips!