Concurrently means that the original parent and its continuation could be executing at the same time, each in its own thread.
Note that the continuation will follow all the child tasks, and each of them only gets executed after it was spawned, so the overlap is only partial, and you probably wouldn't do anything substantial in the original parent after spawning the children.
(Note that "one thread each" and "more than a thread each" mean something else than what I think you intend.)
P.S.: I should probably have referred to recycle_as_safe_continuation() above, instead of just recycle_as_continuation().