MEXIA (September 2, 2010) - The Mexia Independent School District confirms its investigating an allegation a 5-year-old girl was sexually assaulted last week by a fellow student on a district school bus.

Mexia ISD Interim Superintendent John Turpin says the alleged incident occurred last week, and the district immediately launched an investigation after the alleged victim's mother contacted the district.

"Its not behavior we have ever had to deal with at the elementary level." Turpin told News 10.

Turpin declined to confirm the age of the suspect, only saying the boy was under 10-years-old.

"Worst nightmare, I never thought at 5-years-old, she would have to experience something like that." the alleged victim's mother, who asked not to be identified to protect her daughter, told News 10 on Thursday evening.

The district said it immediately had its police department launch an investigation, but because the student was under 10, criminal charges were not pursued.

In Texas, children under 10 years old are not criminally liable according to prosecutors consulted by News 10.

Turpin, with the district, said the student faces punishment, but he could not detail that punishment, citing school policies.

Turpin also said he consulted with school board members right after the incident, and the district decided not to send a note home to parents, believing the incident was isolated in nature.

Turpin says the Texas Department of Family and Protective Services was also notified about the alleged incident.

"I want to be able to protect those other children, I couldn't protect my daughter, but if I could stop it from happening to another child, that is, that is, well worth it." the alleged victim's mother said.