Okay, I gotta go with a slightly different idea.
First off, a dSLR camera just doesn't do a good job of recording audio. It is mostly the mic, but there are other limitations, too. Gain control being the biggest. There are a lot of ways to work around each of the shortcomings, but in my experience, limited though it may be, the more work arounds you use, the lower the quality.
Getting the audio "off camera", much like getting the flash off camera, improves the quality a lot. So, something like a Zoom H1 or the Tascam equivalent is a good way to go. Since you are only doing video of the kids, having it mounted to the camera is a good idea. Zoom makes this, so you could mount it on the hotshoe of your camera. It also has a line out jack, so a simple 1/8 inch male to male stereo cord which you might have or can certainly pick up at Radio Shack for a couple of dollars would turn the H1 into a hotshoe mounted mic with the audio recorded in the camera. Bonus is that you also have an audio recorder you could use in other ways.
Simplest solution? Without a doubt, the Rode VideoMic Pro. Good quality sound and it is compact. Only downside to that is it is double the cost of the H1 and a hotshoe mounting device. And I just ran across THIS, which gives you even more stuff for less money than the Rode VideoMic Pro.
Lots of ways to skin that cat.