Wanna convince your kids there REALLY IS A SANTA CLAUS?? I know how. I've done it. I had my son believing until he was 13 - I so completely convinced him. Here's how step by step.
What you need: 1, Two walkie talkies. Don't use a phone - or cheapo $10 toy walkie talkies. 2, A friend with a car that has a car stereo. 3, A sound effect of wind that will play on your friends car stereo. That's it.
In the days leading up to Christmas announce that you have special information about Santa flying over your house. You also have info of Santas' special frequency in which to raise Santa with your Walkie talkies. At a pre determined time, have your friend park down the street. Have them BLAST the wind sound effect on their car stereo at a high volume. Make the sound effect long, as you have no idea how long the conversation might last. Key the mic and ask for Santa. What comes out the little speaker will blow your mind. The wind effect alone will sell this bit, as it'll be hard to hear Santa over the noise - making it impossible to recognize who Santa might be. Put your kids on with Santa and tell them their time is limited. Instruct Santa to drive away after about 3 minutes. His signal will become more faint as he drives - as if he's really flying over. Eventually you won't be able to hear Santa at all - but your kids will believe with complete certainty that they have in fact actually spoken with the jolly old elf.