Sarah,
One option may be to send directly to those children. If none of them have e-mail addresses we will move up to the e-mail address of the Household. Of course, you could still hit a child's e-mail address that way, but it's a possibility. I know you can always submit a request to the help desk and realize that can take a while if things are busy.
If you haven't done so already, I'd suggest adding a vote to this idea:
http://experience.fellowshipone.com/ideas/idea/archive/2007/12/19/sending-email-to-parents-of-a-participant-child-or-youth.aspx
In Him,
-Peter Schott