Correct call for missed base?

[DaveASA/FED]

As my user name suggests I am a softball guy. I am posting this for a coworker who had a question from a little league game.

Situation:
Batter hits ball deep to outfield, looks like an easy triple. As runner heads to 2nd, 2nd baseman is straddling the bag (ball is still at fence) and runner tries to hit corner but misses base. 3rd base coach sees he missed the base and puts up the old stop sign to send the runner back to second. Runner is slowing down (presummingly to return back to 2nd) when BU calls "Dead ball runner is out for missing 2nd base." Ball is not at second yet, just hit cut off in outfield. Now is this the correct call?

In ASA the runner is allowed to complete his running prior to any calls for a missed base. Also a missed base is an appeal play where the defense has to ask for a call. I agree if the ball was an second it could be a live ball appeal, but it would still not call for the "dead ball" call. I admit ASA and little league are different and I don't know little league that is why I am asking you all. Thanks in advance.