Not sure how you would integrate that sort of thing to the ISA though. Maybe something like:

    00 THR 004 001 @A0
    04 JEQ 001 @A0 010
    08 --- parent thread
    ...
    10 --- child thread

where THR instruction would store a value that is visible only to child in some memory location, in this example value 001 would be stored at @A0, which is then used to distinguish the threads in a conditional jump.