Tantra means technique

It refers to technical aspects of Yoga, which means "union with the Divine".
Tantric rituals are practices which are supposed to awaken the Kundalini energy transforming sexual energies into spiritual energies. These practices are reported to be dangerous.
The "mystical marriage" of the male and female Divine energy must not be taken literal. Kundalini awakening in fact does not involve sexual practices. The Kundalini rises spontaneously and effortlessly - especially with children.