The amount of harm that a 3 year old can do isn't much, but what they can do could be really nasty (biting or poking eyes).

If you do decide to teach some basic self defense, I would do exactly what you say Blast and prepare her for "bad people". But curling up in a ball wouldn't be what I would choose. I would say, scream (or blow whistle), run away, and call out for help. If someone ever did get their hands on her, teach her that biting is okay under some circumstances and that if she can, headbutting the nose or clawing at the eyes is an effective distraction to allow her to run away. There are a few other worthwhile low-force, easy to execute, yet very damaging techniques as well.

The very same things have been on my mind, and I don't think it's being paranoid in the least. People kidnap kids, shoot them, rape them, even cut them out of the womb. It's a sick world full of deviants, but you also don't want your kid growing up afraid of their shadow.

I think for the most part Parents keep pretty close tabs on 3 year olds, but when they are in school or daycare, that's another matter. I would certainly ask your child's caretakers if they have plans for things like this and if they teach kids basic principles (it's unlikely they do at that age).

Anyway, take it slow, and before you teach any techniques or have anyone teach them to her, make sure she's VERY clear on when she can use them. For instance, it's never right to do it when she's just angry. But don't tell her it's not right to bite other kids... There are documented kidnappings and killings by young children and teens

Ah... it's just a sick world. I think it's prudent to be prepared in this manner... just don't treat her like an adult and make sure you go slowly.