I get quite effective results by staring straight at the kids in the eye with a (You're NOT gonna like how this turns out) look, and in a loud, deep and penetrating voice say ONE and stick out a finger. I usually start to lean a little toward my hand, and if I have to get to two, I start moving toward her, and say TWO....
I've never actually made it to 3, I think I intimidate her enough, and she can imagine what will come if I ever actually have to make it to 3...
MAN, I hope I don't ever get called out, I'm not sure what will come with 3...
When I was a kid, 3 was followed by either a belt, or Razor Strop!