add child list to Retreiver class
add child list to Retreiver class

chanchett/ds3_python_sdk,SpectraLogic/ds3_python_sdk,SpectraLogic/ds3_python_sdk,chanchett/ds3_python_sdk,chanchett/ds3_python_sdk_,chanchett/ds3_python_sdk,SpectraLogic/ds3_python_sdk