Mark Salling: Girls Under 10 in Sexual Acts Found in Actor's Computer ... Sources Say

Mark Salling's computer not only contained pics of underage children in sexual scenes, some of the children were under 10 years of age ... this according to law enforcement sources.

As we reported, the LAPD's Internet Crimes Against Children Task Force seized more than a thousand images from the "Glee" star's desktop computer, and they still have to go through his cellphone, tablet and laptop.

Our sources say some of the images involve girls under 10 engaging in sexual activities.

We're told the cops were "100%" they would find what they were looking for based on an interview with a former girlfriend of Salling's as well as other evidence.

Salling was arrested for possession of child porn ... porn involving minors "engaging in or simulating sexual conduct." The Salling family posted $20,000 bail shortly after his arrest and he was released.