A 10-year-old boy shot his sister and then turned the gun on himself, investigators said.
Walker County sheriff's deputies said the shooting happened on Duke Road near Highway 30 late Thursday.
Detectives said Coby Tucker walked into his 15-year-old sister's room and opened fire.
Ashley Tucker was flown to Memorial Hermann Hospital in critical condition and was in good condition on Friday afternoon. She is a student at Huntsville High School.
Detectives said Coby fatally shot himself. He was a student at Huntsville Intermediate.
Investigators have not said how Coby got the gun, but they did say that the family has a gun safe in the home. The motive for the shooting is under investigation.
Deputies said the children's mother was at home at the time of the shooting but was apparently unaware that her son had a gun.
"Once she heard the shots, she responded and called 911," Detective Greg Williams said.
The children's father was at work at the time of the incident, investigators said.
Officials have not said if the parents will face any charges.
Deputies said they have never been called out to the family's home before.
Huntsville Independent School District officials said counselors are available to students or employees who need support.