A Columbia University student whose global campaign against rape and sexual abuse of children earned him berths to speak alongside United Nations and State Department officials was himself charged this week with a series of sex crimes against children.

In a complaint filed in federal court Tuesday against the student, Joel Davis, 22, prosecutors outlined a series of sordid allegations, including an admission by Mr. Davis that he had sex with a 13-year-old boy in his New York apartment.

The complaint also outlines text messages Mr. Davis sent undercover F.B.I. agents seeking sexual images of children as young as 2.

“The conduct alleged against Joel Davis is as unfathomable as it is sickening,” Geoffrey S. Berman, the United States attorney for the Southern District of New York, said in a statement Tuesday.