Really annoyed me that the kiddos voted to not switch, and they got the car. Getting children to understand that 1/3 is smaller than 1/2 is hard enough. I’m going to program my own evil version that only wins on switch the first time next time I do this.
What helped me understand way back when I found out about it was using 3 cards, one car, two goats. Then have the student choosing not see the cards and you and the rest can see them standing on the other side. If the student never switches, he/she has 1/3 chance of picking a car. If the student always switches, it becomes obvious, especially if you see the cards, that to win he/she has to pick a goat, which is 2/3 chance. It makes it even more obvious with more goat cards. The students watching immediately see which card must be chosen for two situations - never swap or always swap.