Wow, McG - that really sucks - nothing's going to bring the dog back, but I sure hope you get some satisfactory closure on the circumstances.
Here's a website that might offer a little ease:
Rainbow Bridge
- its a production of
Pet Loss Grief Support
Among other resources they offer, here's a
great article there with some good tips for helping kids get through the loss of a pet.
And my recommendation is get another dog as soon as you can bring yourself to do so, and make the kids a big part of turning the new dog into a family member.