I agree with black walnut's suggestion. The worst thing that can happen to the children is that they learn twice as much music. Also, you won't have any problems with trying to keep one group quiet while you're teaching the other group their part. As far as dividing them later, the girls should be able to sing either part at that age. If your boys' voices are unchanged, they should too. The suggestion about raising hands could be interesting to try. Theoretically, at this age you should be able to divide based upon QUALITY of the voice and not so much on RANGE. Put those who sound nice on the high part on that part, and those who sound nice on the low on the low. You can listen to them as they all sing each part. Those who are versatile can rove.

cinn