>How do I do to change the order of a child table that is connected to his parent with set relation? Is it even possible (using the SET ORDER command)?

No. SET RELATION cause an implict seek in the child table whenever the record pointer is moved in the parent table. If the order is set to a different tag in the child table, you could find no child records or, even worse, the wrong records.

My suggestion would be to use parameterized views instead. You could requery the view when you moved the record pointer in the parent table and build sorting indexes for your child cursor.