Here is a couple of effects that you can use to entertain some kids, or use in a video production. The first works best with small kids, older kids may figure it out too quick.
The Amazing Glowing Pot!
You'll need a bowl, two tiny bottles, or maybe test tubes, a knife and a glow stick. If possible get a bowl with a shiny surface on the inside. To pull this off you will need to be a storyteller and build the kids up.
Before you start, and before the kids arrive take a pocket knife and carefully cut the top off the glow stick. Inside you will find a liquid and a glass tube with another liquid. Carefully pour the first liquid into a bottle and remove the glass tube. Now break the tube and pour it's liquid into the second bottle. Put the knife and glass away.
A glow stick works because when you bend it you break the glass tube inside and allow the two chemicals to mix. The chemicals glow when mixed together. You will be doing the same for your trick, only you will control the mixing.
Gather the kids together and start telling them your story. The story can be anything but you want the bowl to be important to the story. When you are ready pour the first chemical into the bowl and continue the story. Then for dramatic effect pour the second chemical in and stir the mixture. The inside of the bowl will begin to glow!
This is guaranteed to entertain little kids! Tell them it's magic or a potion. DO NOT touch or drink the liquids! It says non toxic on the package but I wouldn't trust it.
Pesky Ground Varmints!
The other little trick you could play on some older kids but little kids are more fun. It is a story guaranteed to entertain. But you will need to prepare early. You will need a speaker, some speaker wire and a connector. Plus you will need a zip lock baggie that the speaker will fit into. And you will need to make a audio CD.
Here is the gist of the trick. Take the speaker and hook it up to the wires and put the connector on the end. A big woofer works best! You will need enough speaker wire to run to a hidden CD player. Put the speaker in the baggie and close it best you can around the wire. Now, you are going to bury it in the ground. Pick a spot where you can conduct your show and have kids sitting nearby. Bury the speaker about 3 to 4 inches under the sod being careful not to disturb the surface grass.
You will also dig a small trench away from the speaker to hide the speaker wire. If you do this about a week before the night of your show and cover the area back with the grass it should look like no hole was ever dug there. The baggie will help protect the speaker from any moisture or rain.
After you bury the speaker and find a suitable place to hide the CD player it's attached to, make a CD of sound effects or responses. You will need to time the CD audio with your story. Here is the catch, you will need the audio on the CD to start about the time you are ready to really get into the show, or have someone start the CD that is hidden.
If you are doing this alone you will need to time the CD. To time the CD, figure out about how much time you will need after starting the hidden CD player to get your group seated and you start your story. If you time it right you can have the effects begin to bellow from under the ground on cue!
Let's say it takes you 4 minutes to get seated, and get the show started. And you want to talk to the ground and have it start responding at about 6 minutes. Simply record 6 minutes of zero audio on the CD before you start the talk back section of the audio. You can even carry a stop watch and tell the group that it is part of the show, you have to keep a close eye on the time of the story or the ground varmints will become agitated. Something like that. Whatever works.
In reality you are watching for your pre determined time the sounds will start on the CD. When your group arrives take them to the place you have prepared and have them sit. Then go get your magic wand or something like that, in reality you are going to turn on the CD player and start your stop watch. Keeping an eye on the watch go stand by the spot and start your story, build it up with a lot of drama and as you near the precise time the speaker will start sounding off, start talking to the ground varmints!
Here is a basic story idea. Tell your guests you have been having problems with moles, gophers and ground varmints. Then start talking about them and how bad they are and as you state some "fact" about them have the ground respond, "Hogwash!" You will of course look down and pretend to wonder who said that? Have the ground say, "Yeah buddy it's us the GROUND VARMINTS!"
Then just take it from there. Have a funny conversation with the "ground varmints" and entertain your guests. Practice the story a few times before the guests arrive.
If the speaker is sufficiently loud you will have kids coming up off the floor! They will have no idea how sound is coming out of the ground!
After they have been entertained be sure to let them in on the secret and show them the speaker. This way they will not go home afraid or think you have talking critters. Tell them it was all in fun. Let the parents in on it. You should only do this with close friends and never if a parent or your friend would object. Check with parents first!
It will take good timing but the payoff will be hilarious. Have the answers funny or comical. So play with the idea and determine any modifications you want to make to the basic plan.
Remember, you never want to truly scare a child so don't do spooky sounds. A little Halloween prank is fun but terror is not. So don't make your story scary and always reveal the prank. The idea is to entertain and have fun, not scare the dickens out of your guests. Voices coming from the ground could be scary to a young child.
If you pull it off right every kid there will think you have talking ground varmints! They may gather around to listen. Let them. But make sure they don't try digging up the speaker! LOL
Oh, and either turn off the CD or have it auto stop after the "conversation." You are sure to get a fun video out of it too.
Be sure to video the events and Have Fun!