Cuclidus demons were a species of demon known to take the form of human children. They hypnotised other beings into caring and protecting for them in a parent-like role.
In its child form, a Cuclidus demon hypnotized a vampire from Sunnydale. While patrolling, Buffy Summers and Angel encounter the child and the vampire. Angel immediately identified the child as a Cuclidus demon, and with further research from the Scooby Gang, Buffy is given the information to kill the demon.
At Pretty Nails, the vampire is killed by sunlight, causing the demon to hypnotize Joyce Summers instead. At her house, Buffy encountered the demon again, but this time with her mother. By locking Joyce outside and isolating the demon inside, Buffy manages to kill the demon, which in turn restores Joyce back to normal.