CONROE, Texas -

Police are investigating a mother and her boyfriend, after her two children ended up in the hospital.

Staff at the Conroe Regional Medical Center notified police, after a 4-year-old girl was brought in for treatment.

According to investigators, the little girl suffered serious trauma and had to be flown to a hospital in Houston for further treatment.

The little girl was taken to the hospital by her mother, 28, who discovered the little girl injured when she came home from work.

The mother says her daughter was under the care of her live-in boyfriend, Alberto Pedro Vazquez, 21, when she was hurt.

Police said the woman's other daughter, 8, was sent to a different hospital earlier in the day.

Investigators said faculty members at the 8-year-old's school observed facial injuries and were concerned for her health.

Child Protective Services is investigating the case.

Detectives are interviewing the mother.

Vazquez is not the biological father of either child.

Vazquez was arrested and charged with injury to a child.

His bond was set at $500,000.