Girl Guides are like Boy Scouts, it's a lot like herding cats. A helpful hint from an old scouter, try to burn off some of their nervous energy before you get into showing them a few moves. Start them off with a brief talk and as they start to show the signs of boredom just transition right into some basic warm up moves before you show them 'the real stuff', 5 minutes of warming up (for safety so they don't pull any muscles) should get them pink in the face and refocused for the demonstration.

Difficult but important. I do like the meme that suggests it would be easier to teach boys not to rape, but today it's still necessary to teach girls self-defence. I wish I had a good way to make children focus but I'm completely unqualified in this field.

But it’s really important. If it’s better, request that they divide into two smaller classes.