Hi,
What you are describing is the nested Handling Units.
You can pick the child HUs either through LT12 or LM47. You can either select the whole child HU or partially from child HUs.
Pls look at (For LM47) Pick and Pack - Nested Handling Units - Mobile Data Entry (LE-MOB) - SAP Library
For LT12 Handling Unit Management (LO-HU) - SAP Library
Thanks.
Jogesh