Mrs. Ogre,
I am absolutely shocked! I ride public transit every day to and from work, and I have never, EVER had someone do something that crazy. Wow.
In order to protect myself, I usually avoid eye contact and staring or scowling at other passengers, even kids. That way, if one of them does something stupid or rude, I can very honestly say "What's the problem? I was just sitting here minding my own business."
I do try to smile at people if they've kept their kids quiet and still the entire ride. It's a silent "thank you" for respecting my space and my peace of mind.
If possible, I will also change seats to accomodate parents and children, but my motives are more selfish than they imagine...it gives me the creeps to be physically close to kids, and I am much more comfortable sitting as far away as possible! I play it off as an act of politeness, however, so everyone wins. I look good, they get to have a seat, and no one goes postal!
As far as your story goes, that's just rediculous. I mean, gosh, even the drunks on the bus here have better manners than that breeder and her sprog. Shame on them!