The song of the music box is "Greensleeves", also known as the Christmas carol "What Child Is This?" The carol's title also serves as a question about the central mystery concerning the child observer character--who is he? What child is this.
The Observers are ectogens - persons who were, or are being, gestated in artificial wombs.
The coded glyphs at the commercial breaks spell out GRACE.
When Donald is telling how his kind are created, we are shown several stages of the gestation. The first stage shown is the same fetal image that has been part of the apple glyph since Season 1.
This episode takes place in 2036 and 2609