Giving a little "Magic show" about Mobius strips might be fun. Make a huge number of mobius strips and cylinders, and hand them out to the kids along with safety scissors. You could have a predrawn "center line". Ask them what will happen when they cut along the center line: How many pieces will you get? They will probably say two for both shapes. Have them cut along the line and see what happens! The result for the cylinder is as expected, but for the mobius strip you get a piece of paper with two twists. Now ask them what happens if they cut this in half. You get two interconnected links! You could have them start with a new mobius strip and cut halfway between the center line and one edge, following their way around. You get a mobius strip linked to a double twisted strip! This will all be great fun for the kids.
You can "explain" some of these phenomenon phenomena by showing them how to make a mobius strip themselves: just take a strip of paper, twist it, and tape the ends together. From this perspective cutting a mobius strip in half is just the same as taking two strips next to each other, twisting both of them, but the head of one piece attaches to the tail of the other, so you can see how cutting the strip in half only leads to "one piece". It might help to have some different colors of paper, so they can more easily keep track of the "two halves".
You could show them some Escher drawings involving Mobius strips - the one with the ants would probably delight them.