Katrina Herrador, 21, of Fairfield, a program leader since May in Vacaville's Teen X-treme summer camp program, was arrested Tuesday for having sex with someone under age 18, Sgt. Denise Quatman said.
She was removed from duty on Friday and resigned on Monday, Quatman said.
Herrador became acquainted with the boy who attended the camp sessions, Quatman said.
Herrador allegedly had sex with the boy late Thursday evening at her home, Quatman said.
The boy's parents discovered a suspicious text message early Friday morning that caused them to suspect an unlawful sexual relationship between Herrador and their son, Quatman said.
It does not appear there was any misconduct or criminal activity during the summer camp program sessions, Quatman said.
Teen X-treme is a summer camp for teens in grades six through nine. It includes arts and crafts, sports, field trips and swimming, according to the City of Vacaville's summer camp web site.
Anyone with information about any inappropriate behavior involving Herrador with the boy or any other summer camp participants is asked to call detective David Marsh at (707) 469-6616.