The Haunting of Hill House

A litter of cats dies from disease (presumably). There's a scene where a bug pops out of the dead kitten's mouth (very clearly not a real animal) and another scene where the kitten has zombie eyes.

Dead kids plus you watch one kid puke after being poisoned.

Tiny part of story: pregnant character rots

You learn through dialogue that Mrs. Dudley loses a baby (stillbirth)

Minor part of the story and it's implied except when Theo is venting about her day to her girlfriend.

One character's monologue seems to describe her hurting her children.