Well, i find that relating to the kids helps.
If they understand what you are saying, and it appeals to them, they will be more interested in the magic you are doing.
Ive got a magic gig tommorow for kids and i try not to plan too much, i rather just have fun, and that usually works for me.
I have found that tricks from Art of Astonishment (Paul Harris) are very effective.
Examples are Reset, since the effect is simple yet effective, headache, which can be funny if performed in the right approach, and hi there babycakes since it has a very nice effect, and is a surprise since they are holding the card when the magic happens.
I find that the tricks aren't as important as you might think, i feel that the attitude of the performer is a lot more important than the actual affects, just remember tha aim of the game is for them to have fun, thats all kids care about :-)
You have to make yourself out to be the fool, the silly guy etc.
I also think that tricks where you apparantly fail but then pull it off even better than expected are very good among childrens shows.
Just a few thoughts :)