'Bumfights' Creators -- Busted For Mailing Baby's Head ... And Other Body Parts

The co-creators of the "Bumfights" video series were arrested in Thailand over the weekend for allegedly packaging child body parts stolen from a hospital, and shipping them to the U.S. ... labeled as "toys."

According to multiple reports ... Ryan MacPherson and Daniel Tanner were busted when a scan of the boxes by a Bangkok parcel company revealed the gruesome discovery.

The 3 boxes -- reportedly intended for friends in Las Vegas as a prank -- contained several body parts ... including a child's foot, an infant's head, an adult heart and 2 pieces of adult skin.

Both guys were taken into custody and questioned by cops, but were eventually released for lack of evidence. They've since fled to Cambodia.