Actually, the Kit 1s distributed to the children were a little bit rigged.
The Kit 1 that the staff member had made beforehand had an NSK bearing set into it as a part supporting the rotating shaft. But the kits handed out to the children used a part made from polystyrene board instead of a bearing. The reason the shaft would not spin as fast was the strong friction between the shaft and the part supporting it.
When asked what was different between the first Kit 1 and the Kit 1s they assembled, the children shouted out, "The weights!" "The shaft!" Although they were looking in the right place, they didn't quite get to the correct answer.