On my third trek to the grocery store today (I'm baking a lot for a breakfast at Eldest's school tomorrow) I ran into a father of four. In response to my inquiry about how life was going he replied, "Well, you're only as happy as your least happy child."
I felt his pain, but said I wasn't sure that was entirely true. After all, when you're a parent you have to embrace the fact that life consists of many mixed feelings at once. The sadness over one child gets mixed in with the I can't believe he did that! over another, and folded into the joy of seeing yet another kid finally succeed. Life as a parent ceases to be either/or, and transforms itself into both/and.
Part of this is mixup is because (shhh!) we're no longer in control. We have influence over our children's lives, but we don't have the autonomy with them that we have with ourselves.
Frankly, I think this is part of the reason we're told to be fruitful and multiply. Kids help us down the path to humility. They force us to admit we can't do it all, can't control everything, and can't make everyone happy.