HI Vimal,
Please use this sample code as a solution.
lo_svc_mngr TYPE REF TO /bobf/if_tra_service_manager.
lo_svc_mngr = /bobf/cl_tra_serv_mgr_factory=>get_service_manager(<BO_KEY>).
CALL METHOD lo_svc_mngr->retrieve_by_association
EXPORTING
iv_node_key = <node_key-root node>
it_key = lt_key<ALL the key of root node for which you need child node information>
iv_association = <Association of root node to your child node-key>
iv_fill_data = abap_true
IMPORTING
eo_message = lo_message
eo_change = lo_change
et_data = <lt_data><table type of your person involved combined structure>.
Thanks
Praveen Gupta