I'm very sorry that the young girl had to endure such an attack, but I agree with previous posters that I think the parent is partially to blame for:
1)brandishing his child with a sign, making her the focal point of his own political agenda(and I'd say the same if it was a Kerry supporter)
and
2)allowing his child to be further exploited by the public as the latest example of the dirty damn awful liberals violent outcry against Bush
Not knowing the exact circumstances of the encounter, I have to wonder if the parent didn't know beforehand what he was walking into, and have an idea of what might happen. Of course, that doesn't make the individuals who attacked the girl any less disgusting.