KenpoSterre said:
you could invite and instructor to come but make him look like a totall thug. Dom't tell them the thug is a instructor. Have the thug attempt to attack a child but you come and rescue the child. Beat the crap out of the guy (make sure the guy has a cup and breastplate on They will be scared silly and won't make trouble. Make sure the parents know because if they interfere....
As much fun as this might be to contemplate, I would not suggest it. I suspect that most, if not all, of your students would be pulled by their parents, and you run the risk of someone else (parent, student, or someone not related to your class) trying an attack in a fashion that leaves you no choice but to hurt them.
I have taught young kids in the past, although my current class has no students under 11. The key to teaching small children is to keep them busy, so they don't have time to be bored, and therefore to lose their focus on you. Change activities often, and make sure that those activities involve lots of movement and very little talk. If you have information you want the kids to know (stances, techniques, patterns, knowledge, etc.), make a game of learning and repeating it, and as much as possible, have the students demonstrate it rather than say it. Make games out of demonstrating techniques - relay races while performing kicks, target practice (hands or feet) using ping pong or foam balls (either trying to hit them across the room, or suspended from a string so they don't fly all over the place), etc. Think about the games you played as a kid and modify them to make use of MA techniques instead of whatever they started as - for example, have the kids play tag, but require that the tagger use a specific technique or type of technique.
Also, make sure that the rules of the class are clear in advance - have them ready, in easy to understand language, in writing, to give to new students when they enroll, so that they (and more importantly, their parents) know what the expectations are - also post them, in large letters, somewhere in the facility where they can be easily seen during class.
For all ages, but especially young children, the key to controlling their behavior is consistency - the rules must always be the same, and they must always be enforced the same way. At the same time, you need to make sure that the rules are realistic: these are young kids, of course they will be distracted by activities going on in the rest of the room. Perhaps you could work something out with the gymnastics class to use some of their equipment on occasion; that will take some of the mystery, and therefore the interest, out of watching others use it. I have used gymnastics equipment in the past for teaching TKD - balance beams, for example, are a great way to teach stances, the mats under the equipment is great for teaching rolling and falling, and so on.
Kids can be a lot of work to teach - but also a lot of fun. Let us know how it's going, and enjoy!