Here's a great self-working card trick to teach your kids. If they are old enough to spell, they will love performing it for their friends. I learned about the trick, which was invented by magician Jim Steinmeyer, on Greg Ross's Futility Closet blog.
"Remove any nine cards from an ordinary deck, shuffle them, and deal them face down into three piles. Choose any pile and note its bottom card. Then assemble the three piles into one, being sure to place the chosen pile on top.
Suppose the card you chose is the three of spades. Spell T-H-R-E-E, dealing one card face down onto the table with each letter. Place the remaining cards on top of these five and take up the whole packet. Now spell O-F, and again place the remaining cards on top of these two. Then spell S-P-A-D-E-S and place the remaining cards on top.
Now pick up the packet and spell M-A-G-I-C, dealing the final card face up. It's the three of spades."
It boggles my mind that Mr. Steinmeyer could invent such a trick!