In the '80s if you were a vampire, you had to go to New Orleans. It was the whole Anne Rice domination of the genre, and its dark romance was very attractive to those who wanted to join the world of the undead. When a young man who took the name Eccarius became a vampire, he immediately moved to New Orleans and played the part to the hilt - he wore Victorian clothes, drank blood from crystal goblets and slept in a coffin. And he found a group of hangers-on.
They were all disaffected youth, lonely young people who thought death was romantic and beautiful but weren't exactly ready to commit themselves to it. Becoming a vampire was a good middle ground, and until they could become vampires, they could at least hang out with one.
They named themselves Les Enfants du Sang and gathered in a dark basement warehouse. They wrote bleak poetry and wore black clothes. The more committed among them cut themselves and allowed others to drink their blood. And they took themselves very, very seriously.
Which is why the arrival of Cassidy threw them into such chaos.
Cassidy was a vampire-like their beloved Eccarius but was otherwise completely different. He was a hard partier who loved humanity, ate real food and drank beer, loved the physical pleasures of the world and had no time for the quasi-romantic trappings of Les Enfants. He quickly took Eccarius away from them, first symbolically by encouraging him to be more human, and then literally, but staking him to a church roof to burn in the sun. Eccarius had taken to using Les Enfants not only as an ego boost but as a blood source, something that Cassidy - no saint himself - found morally reprehensible.
When Cassidy left, Les Enfants were in tatters. The less committed members left, but a few of the hard-core stayed on, looking for the chance to become the immortals they'd always wanted to be. When Cassidy returned to New Orleans some years later, this time in the company of Jesse Custer and Tulip, they made their move. Unfortunately, most of their moves were mistakes.
They tried to kidnap Tulip and discovered that she was very capable of taking care of herself. She killed at least three of them and escaped their headquarters without too much trouble. Better armed and prepared, Les Enfants tried a second attack, this time at a cemetery where Custer was undergoing a voodoo ritual. This time they were marginally more successful, in that they did manage to decapitate Cassidy. This didn't kill him, though, nor were they able to kill Tulip or Custer. In the fight, nearly all of Les Enfants died.