Childhood's End (S01E05)

During an exploratory mission, the puddle jumper’s electrical systems are knocked out by a massive electromagnetic field and the team is forced to make an emergency landing. They soon encounter a primitive tribe of children who have been untouched by the Wraith for centuries due to the protective force of the electromagnetic field. But the children believe it is their ritual of mandatory suicide at the age of 25 that keeps the enemy at bay, despite the contrary insistence of the Atlantis team. Fearing the “full growns” in their midst will attract the Wraith, the villagers become anxious for their unexpected guests to leave as soon as possible. But to be able to leave, Dr. McKay (David Hewlett) must first disable the electromagnetic field. In doing so, he unwittingly trips a Wraith silent alarm, leaving the tribe open to attack. (iTunes)