We attempted to use our older kids (8-10 year olds) in our local church to help tell the story of Saul (see week 21's script). This methodology is especially useful in connecting older kids to the process and giving them a job (albeit a small one). We've done this at other times with good success. It went okay, but I have a few tips if you ever choose to use this methodology.
1) Don't let them read the script cold. When we've had them practice beforehand, things go MUCH smoother, and there is less of a tendency to goof around up front. So, find a time beforehand that you can let the kids practice.
2) Lay out the expectations. Again, for less goofing.
3) Keep the content light and fun! This method works well when the script is fun rather than serious and dire!