The narrator states that at the carnival, Denver, Sethe, and Paul D "were not holding hands, but their shadows were," implying that while this newly-formed trio is not yet a family (Denver, especially, has not yet accepted Paul D), they certainly have the potential to become one. Their "shadows," or some version of themselves, have coalesced and joined forces. Sethe herself sees their shadows and "decided that it was a good sign." They are described as "gliding over the dust holding hands," as though they were no longer tethered to the earth, but floating above it. In this way, the shadows seem to be symbolic of the bond that will eventually form between the characters, and the lightness that a human connection can provide to those who have been so long denied one; by the end of the chapter, even the once-reluctant Denver is "swaying with delight."
It is true that the three shadows holding hands could foreshadow the possibility of a life comprised of Sethe, Denver, and Paul D. However, the fact that Morrison mentions it repeatedly makes it seem as though we ought, perhaps, to consider it more deeply. Furthermore, the fact that the narrator describes the shadows cast by these three individuals, rather than just the individuals themselves, seems to suggest that it is not the relationship among these three particular individuals that is being foreshadowed. When they return home from the fair, Beloved is waiting on the stump outside the house for them, and it is the relationship among the three women, chiefly, that will move the plot forward for the remainder of the text.
We tend to associate shadows with both literal and figurative darkness. If we describe someone as having a shadowy expression, or if their eyes are shadowed, we are suggesting that not all is as it seems. Thus, the shadows that seem to be holding hands, which appear to represent Sethe, Denver, and Paul D, might actually foreshadow the darkness coming—the darkness that arrives with Beloved.
The carnival scene appears to be a symbol of normalcy, and of family. Paul D. is in high spirits there, and his exuberance influences both Sethe and Denver;
"no one, apparently, (was) able to withstand sharing the pleasure Paul D. was having."
The repeated references to the shadow of the three of them holding hands is a sign of hope. The image symbolizes unity and cohesiveness, and foreshadows that perhaps Sethe and Denver, with Paul D., might one day become a family.
Sethe in particular takes note of their shadows. It causes her to entertain the thought that
"...maybe...it was a good sign,"
and consider that they, the three of them, might at last find
"A life. Could be."
Denver, who is so insecure and jealous of her mother's attention, also finds that her doubts and fears that Paul D. will be a rival for her mother's affections are lessening. "Soothed by sugar" and the kindness that Paul D. is showing her, Denver, for the first time dares to consider that "Paul D. (isn't) all that bad," and that the three of them might work out after all.