John Ott, 67, faces up to 30 years in jail and a $250,000 (Sh20 million) fine when he is sentenced on July 26 after admitting to a harrowing catalogue of crimes.
The Justice Department stated Ott had also started an orphanage in Kenya during his time in the country.
His victims ranged from nine to 17 years old.
Ott admitted he frequently paid for schooling and offered financial support to his victims.
Ott has been in federal custody since he was arrested in December 2012, following his deportation from Tanzania.