ND...as a parent with small kids...i think about this a bunch.
After cnsulting with T, the "best" advise is to teach your kids to speak up and use their "big" voice. A kid that speaks up is and is vocal with a potential perp is "safest". unfortunatly we can not be everywhere and protect them form everything, but we can teach them the skills to protect themselves.http://www.stopitnow.org/
is a good place to look.
One last point, and you express it well....It is very important for us NOT to say we would harm anybody who would harm our children...I do feel if somebody hurt my children I would not take it well at all...but it may prevent them from saying anything if they think mom or dad will "kill" or "hurt" a perp...add into the fact that most perps are known to the victim, it makes sense that they wont want to get a person they know hurt or killed.