Alright. I'm going to try to limit my answer to my limited practical experience.
Experience with kids that aren't mine.
Other kids where my two children go to DayCare remember me from Halloween, when I dressed as a wizard and did D'Lites. That sees to work.
They also get excited when I produce a red silk from an empty hand.
Kids love balloon animals. I don't even have a very large knowledge of shapes, but the kids don't care. Butterflies, swords, teddy bears, dragons, basic hats and basic dog shapes in different proportions are all I can do. Use a black balloon for the hat, turn it "sideways", and complement it with a sword: instant pirate costume.
Experience from my own kids.
All of the below comes with the caveat in mind that they see a lot of it, having me in the house. This has no doubt exposed them to more and increased their curiosity beyond a kid's party audience.
I asked my 6 year old what his favorite trick is that daddy does. "When you drop the cup through the other cup." He was speaking about the cups & balls routine. I find the kids pay more attention to cups & balls when I stress the
magic wand more than the balls, and keep things moving briskly. Dropping one cup through another also goes over very well with both of them.
I actually get away with a lot of classic stuff as long as I do it quickly. Not rushed, but excited and upbeat. Linking rings. Don't leave any rings within reach, however. Silks. A wonder box and a gimmicked color-changing silk go over best when they see "the squares."
Professor's Nightmare for my kids in particular: Count "Big, Medium, Small" twice. Do the magic. "They're all the same size!" Then skip any proof with any other counts, restore them, and show them again. "Big, medium, small!"
Think about them repeating your tricks. Levitating is bad. When they can't figure it out they'll try to jump off something. Yes. Personal experience. My kids have walked in on me practicing rope through neck and loved it. It's quick, flashy, and impossible. But... um... I don't want them getting a jump rope and trying that either.
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The oldest has only busted me one and a half times. Once was the terrible, infamous leg disappearing behind a towel. (It was bath time. I was bored.) The half was in doing Pressure. He started trying to do it too, and halfway even got it to work. But having the full routine plus the bonus stuff here at T11's forum does enough to even keep half-busted from going all-the-way busted.
Crazy Man's Handcuffs could be a fun thing to do when not formally performing. Maybe in between twisting balloon animals with all the kids up close.
The one thing I did not bring up is cards. The only success I have had there is a quick effect with their card reversed in the deck. Not a full Triumph routine. Just a quickly reversed card. If by chance you know the kid has a favorite card ahead of time then it helps to make sure he or she draws that one.
So.. most of this is me entertaining my own kids on the weekends. It may in fact be very specific to these two kids. Flashy, impossible, and performed at the speed of a five year old attention span serve me best.