Right, gonna post this before I forget! We had a Halloween party in, well let's face it - that would be October! One of the Dads performed this trick for a few of the kids and they loved it....
Take 2 mugs and discreetly pad the bottom of one with kitchen paper and dampen. Call the kids in, place 1/2 inch of water in the mug without paper, pour the water from one mug to the other, then attempt to pour it back! Then sit back and enjoy the adulation!!
Give it a go!