What does this line mean, why is it important? "They sank Chicken Little in between his grandfather and an aunt."

The novel Sula by Toni Morrison tells
the story of Sula and Nel, two childhood friends who grow up in Medallion, Ohio. The are
black girls who grow up differently, but who share a deep, life-long connection. One day
when the girls were still quite young they were playing by a lake with a little boy
known as Chicken Little. Sula was swinging Chicken Little around by his arms, but her
grip slipped and he landed in the lake. Unable to swim, he drowned. The girls were
afraid of what had happened and didn't report the event to anyone, so it was several
days before Chicken Little's body was discovered. Sula was upset and Nel did her best to
assure her that it was an accident. After the funeral they seem to have been able to put
the horrible event behind them. The quote in your post tells what happened to Chicken
Little for his burial. He was a poor black boy who had little family, so the townspeople
did what was expected of them and they buried him between his grandfather and one of his
aunts. I think it is important that they "sank" him because the word has a colloquial
feel to and it plays off the idea that he sank in the lake. The memory of what happened
also sank into nothingness for Sula and Nel.

The memory
resurfaces in the final chapter of the novel when Nel goes to visit Sula's grandmother.
Eva is very old and seems to be confused through their conversation, but she does accuse
Nel of letting Chicken Little drown. Nel is shocked that she knows and tries to defend
herself by reminding Eva that it was Sula that held his hands and then lost her grip --
Nel was only a bystander. Eva doesn't let her off the hook though. She rightly comments
that Nel stood there and not only saw what happened but that she "watched" it happen --
implying that Nel didn't do anything to help Chicken Little and therefore she is as
"responsible" as Sula ever was. Nel never looked at that way, but the comment makes her
reflective, and ultimately, she comes to a better understanding of the sunken memory,
and of her complicated relationship with Sula.