I think the issue should be do the kids wearing the kirpan have any knowledge of its significance etc... I have never heard of a case were the kirpan was used in a violent act. But i have come across where the presence of the Kirpan was enough to keep gangs of bullys or racists of these youngsters and teens.
Once i was with an amritdhari friend of mine walking in the evening and a group of white youths were gathered im guessing they had been drinking. So basically they began to shout some racist abuse the usual " taliban, ****" stuff. Now the group had started to walk towards us shouting abuse, so i was thinking we were gonna get our heads kicked in. But when they seen friends kirpan though it was covered it was pointing out from the bottom of his jacket. and when they seen the kirpan they stopped we carried on walking, they just stood there and shouted a few more abuses.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-sikhi-sikhism/29173-let-sikh-pupils-wear-ceremonial-daggers.htmlReference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=29173
All in all now if he never had a kirpan the story could have been alot more tragic. 15 guys vs 2? you can do the math