This will still not give you the behaviour you would expect. Although the transaction will propagate to the child orchestration, it won’t go any further. If the child orchestrtaion calls a web service or sends via the SQL adapter the transaction does not propagate to these. The send port is separated from the orchestration by the messagebox, any error will not rollback a web service call or SQL adapter send.
You will need to introduce a compensation block and have undo functionality. Or some other mechanism to provide transactional integrity.