HOUSTON — Two 10-year-old boys have been arrested and charged with sexual assault after authorities reviewed a security videotape from a Houston school bus that they say shows the boys engaged in inappropriate activity with an 8-year-old boy, police said Tuesday.

The alleged assault took place in August but the investigation took several months, with the 10-year-old boys being arrested last week on a charge of aggravated sexual assault of a child. All three boys are special needs students, and authorities weren't releasing their names because they are minors.

Houston police spokesman Kese Smith said Tuesday it is not unusual for investigations that involve juveniles to take time to complete.

"The length of time is not atypical in investigations of this nature," he said.

If convicted, the two boys charged in the case could face a sentence of up to 40 years. But prosecutors were to later decide whether they will pursue such a sentence or something less.

It was not immediately known if the boys had attorneys. A community activist who was working with the families of one of the boys who was arrested and the 8-year-old alleged victim did not immediately return a telephone call Tuesday seeking comment.

Jason Spencer, a spokesman for the Houston school district, said the alleged assault first came to the attention of officials after the district's transportation department was asked by a parent on Aug. 30 to review conditions on a school bus that transports special needs students to an elementary school. The review was unrelated to the incident.

While reviewing a security video from Aug. 25 from the bus, officials saw what appeared to be three students engaged in inappropriate activity. Authorities didn't provide specifics about what the video showed.

The school's principal reviewed the video, took disciplinary action against all three students and turned over the video to Child Protective Services and Houston police, which led the investigation. Spencer declined to say what disciplinary action was taken against the students.

"We feel the principal handled the situation appropriately and she followed the right procedures," Spencer said.

The Houston school district said in a statement that counseling services were being offered for students involved in the incident. Smith said the parents of all three boys were allowed to be part of the investigative process from the beginning. The family of the 8-year-old boy transferred him to another school after the alleged assault, according to the school district.

Spencer said the school district is reviewing how it handled the case to determine if any policy changes are needed.