Children's book--probably read in the mid-80's. Girl moves into a new house with her parents and triplet siblings. She is suspicious of the previous owner (deceased elderly woman) and investigates, eventually finding buried bodies in the backyard beside a fence. The book had a few sketch-like illustration of the sort a child would have drawn.
Dorrie’s Book, by Marilyn Sachs? I think the bodies in the backyard are imaginary… Dorrie keeps a journal and keeps writing in it as if everything is true, but she’s really trying to get attention because of the triplets taking up all her paren’ts free time.