''The Green Knowe Chronicles'' by Lucy M. Boston is about a boy who ends up being sent to live at an old gothic manor. Strange things are afoot, however...
* The titular children are ghosts that are trapped there. Although the children themselves are benevolent, there's a tree in the garden which the children called "Green Noah", inhabited by a demonic tree-spirit. The little poem about Green Noah is especially creepy:
-->Green Noah, demon tree,
-->Evil fingers can't catch me!
** Oh, children's rhymes are nothing compared to the GypsyCurse that a mad witch originally used to summon the demon into the tree:
-->Scritchit, scratchit, shapen yew,\\
Devil's image, take on you,\\
Evil grow, evil be,\\
Green Noah, demon tree!
* In the fifth book, when Melanie sends a curse to Tolly's grandmother, carved on the skin of a child's hand.
** The maggots and snakes also count as this.
* The scene in the sixth book, when the Saxons are slaughtering the Britons.