One of my ancestral families and all their children and their children's spouses are buried in the same rural cemetery. The only exception is their daughter who died in her teens and is buried in a separate cemetery. The parents died in the 1880s and the other children died between 1895 and 1920. The daughter died in the 1860s before the cemetery where the others are buried was established.
Never assume just because it looks like all of a family is buried in one cemetery that that they all are buried in one cemetery. There could be another child or sibling permanently lurking nearby.