hey i am brand new on here but i know what you are talking about. i am 22 years old and when i get a new routine together i like to perform it in front of my little cousins (8 of the little buggers) they work perfect because they all for the most part have different personalities for me to deal with. sorry for the long thread, but i have a lot to say.
the first category is the middle kid. i have 3 of those to deal with and its always hard. they are the ones who want to have the attention on them and when you are holding it, they get pi**ed. i have found that if you somehow include them into the beginning of the routine they get their fill and shut up for the most part. even if its a simple pick a card trick.
the next ones are the ones who want to ruin your show. this would be my little cousin Casey

(basically a mini Paris Hilton, just waiting for her to go to jail too) the trick with her is to position yourself away from her and seat her behind the others so if she randomly decides to jump up and come around to destroy the trick, you have enough time secure anything needed.
third is the group of kids who dont believe you and insist on knowing how you do it. these are the ones that make up the majority of my group. They understand not to mess with me during the presentation but i have to pay them off in a sense. with these kids i get them to quiet down and enjoy the show by telling them if they are good i will teach them how to do a trick of their own at the end of the show. usually nothing special, but at least entertaining like sticking a straw up your nose and out your ear. they really seemed to love that one. but i at least use it in the performance first.
finally is the type of kid who every magician loves and that is the shy believer. i have one named holly who i love to death because she is calm enough and so wide eyed that i can perform all of my close up tricks for her. like the dollar bill float and loops butterfly. she is always happy to see anything i can do and really believes i am magical. she is the main reason i keep doing magic, because to see the light in her eyes when something happens is more rewarding then anything. these are the people who help boost all magicians and their enjoyment is our purpose.