What does 무동(舞童) mean?

무동(舞童) literally means "dancing child" and refers to boys that used to dance and sing at banquets and celebrations in old Korea. It also refers to the children that sometimes sit and dance on the shoulders of the gong player in a folk band. The only reason I mention the word is that there are two idioms that use it:

• 무동을 서다
  stand on a person's shoulders
  -
• 무동을 타다
  sit on a person's shoulders

The literal meanings of the two idioms are "stand on a dancing child" and "ride a dancing child," which are confusing because I thought it was the dancing child who was doing the standing and the riding?

Here is a drawing of three men doing 무동서기.