'Sesame Street' Composer Fernando Rivas -- Accused of Cuffing Naked 4-Year-Old, Taking Sex Pics

A Grammy-winning composer who worked on “Sesame Street” has been charged with making and distributing child pornography -- after allegedly handcuffing a 4-year-old girl, naked, and taking pictures.

59-year-old Fernando Rivas appeared in a South Carolina federal court yesterday -- where he pled "not guilty," according to the Charleston Post & Courier.

Rivas was arrested back in April -- after FBI agents raided the composer's home and, according to court docs, the feds claim they discovered a collection of photographs ... depicting a 4-year-old girl naked and “restrained in handcuffs and other bondage-type devices."

According to the report, cops say Rivas -- who also taught music at a local Charleston school -- admitted to officers that he took the pictures of the little girl and emailed them to two other sickos.