Threat of violence emailed to schools, do you keep your kid at home?

Hey dads, my wife and I got an email from the school district this morning saying that someone had emailed threats of violence to a lot of schools in my county.

They said there will be a police presence at all schools, and they don't think the threats are serious.

My wife and I are keeping our son (6) at home today because we're just not willing to take that risk. Are we being overly cautious given what the police say? What would you do?

Edit: Here's an article about the threat that I just saw. Seems like it really was a stupid hoax.