An Explicit Multi-Threading (XMT) system and method is provided for processing multiple spawned threads associated with SPAWN-type commands of an XMT program. The method includes executing a plurality of child threads by a plurality of TCUs including a first TCU executing a child thread which is allocated to it; completing execution of the child thread by the first TCU; announcing that the first TCU is available to execute another child thread; executing by a second TCU a parent child thread that includes a nested spawn-type command for spawning additional child threads of the plurality of child threads, wherein the parent child thread is related in a parent-child relationship to the child threads that are spawned in conjunction with the nested spawn-type command; assigning a thread ID (TID) to each child thread, wherein the TID is unique with respect to the other TIDs; and allocating a new child thread to the first TCU.