TMZ obtained these pics from sources connected with the L.A. County Dept. of Children and Family Services ... and they purportedly show 4-year-old Bob Sheen before and after a visit with Brooke Mueller ... we've learned Charlie Sheen believes it's proof she's NOT a fit parent. DCFS sources tell TMZ, Denise Richards -- who has temporary guardianship of twins Bob and Max -- included the before/after shots in her letter to DCFS, claiming a photo was taken just before Bob was dropped off at Brooke's place on July 26 ... and the other taken after leaving Brooke's care.