[qb45]

Complete lyrics (is DMCA coming at me?):

  Inchworm, inchworm, measuring the marigolds
  You and your arithmetic, you'll probably go far.
  Inchworm, inchworm, measuring the marigolds
  Seems to me you'd stop and see how beautiful they are.
  
  (Kids Singing: 2 & 2 are 4, 4 & 4 are 8, 8 & 8 are 16, 16 & 16 are 32)

Nothing to do with imperial units at all.

Even if she didn't know the song, she might have learned 16+16 from those.