Harriet, you’re not saying what your concern. I understand you think the song your baby sings is immoral. However, your child expresses the song innocently and stopping him or her would only make them wonder what is wrong with the song when adults around her dance and sing along the song.
Farmer is a coded song beyond the comprehension of a three year old. Leave the child enjoy the song. She is only a child.
However, beware what television content is exposed to your child. Ensure you’re best of friends with her so you’re the first point of contact when she has any questions or doubts. Don’t allow inhibition to develop in your child.