A Neurolinguistic or Musicological Question About Toddlers

What is it--about language or the brain, or both--that makes my 21-month-old son calm down when he hears children's music but not necessarily when he hears other nice music? For example, I can be playing a nice classical piece with words (like "Jesu, Joy of Man's Desiring," which we had playing in the car just yesterday) and he will be in the back seat fussing but if I turn on music with childlike voices (like an old Disney cassette we have in the car) he immediately quiets down and becomes very attentive. Why? Is he unique or is this how most small children function with "baby talk" in music?