I once heard a therapist say that parents are often surprised by the darkness of their thoughts toward their own children at times ... and that this is normal. It is the old - what you do with it - thing coming into play.
To that end, here is a great and timely link to Urban Mamas (a wonderful resource for metro Portland area parents and others) with a discussion for all us parents who have ever had dark thoughts, lost their temper or thought they just might...
If Mama Ain't Happy (check it out)! I'm gonna when I've got a few minutes to really read.