I seriously cannot imagine what YOU went through as a parent. The fear must have been completely overwhelming. I am so sorry that something like this happened to you. I think the girls should be expelled IMHO. Let the parents deal with either homeschooling them or paying for private school. Either that, or the parents should pay for all those emergency services. Every drop of gas put into a helicopter or a police vehicle. Is your son okay or is he still frightened over this ordeal?
But, you know these lock-down drills got some of these kids very jumpy. Last week I had to return my son to his class to retrieve his homework, and I knocked on the rooms outside door and peeked through its windows, and two girls dove under their desk thinking I was an intruder.