The bodies of a woman between 20 and 30 years old and a boy thought to be about 10 were found in one part of the home, Houston police Sgt. John Chomiak.
The bodies of a young boy and girl were found in another part of the home, described by authorities as a simple wooden structure that was divided in the middle by the porch.
Investigators declined to speculate on the causes of death, although they said there were no obvious signs of a struggle. They also declined to release identities of the victims.
Houston police Lt. Dan Harris said a neighbor became concerned after seeing one of the family's bulls running around unattended in the wooded area near the home.
Neighbors described the victims as a private, Spanish-speaking family who lived on the property for the past six or seven years. The father had built the home himself.
The man was last seen alive as recently as Friday afternoon, witnesses told police. Next-door neighbor Sally Potts said the man and the girl walked one of the family's four dogs on Thursday.
Potts said she hadn't heard gunshots, arguing or unusual noise coming from the house.
Besides the dogs and bull, the family kept a horse and several goats on the property, neighbors said.