 It is about the lead female character, Truly.The first time we hear the music to the song is when Truly (played by Sally Ann Howes in the film) motors up to the Potts' windmill with the children.It is later sung to her by Adrian Hall and Heather Ripley (as Jeremy and Jemima), the twin children of widower Caractacus Potts (played by Dick Van Dyke in the film), and she sings the second verse back to them.