The Lost Boys, also known as The Lost Ones, are supporting antagonists in both the first half of season 3 and the second half of season 6 in the TV show Once Upon A Time.
They are based on the group of characters from the same name from the play Peter Pan. They also take place of the attracted children from the "Pied Piper of Hamelin" fairytale. This gang was first formed when Peter Pan became lonely in Neverland and as the Pied Piper, he traveled to the Enchanted Forest and started luring boys to him by playing a song with his flute. These boys felt lost and unloved by their families and were drawn to Pan. While they were in Neverland, they were basically immortal and never aged. The gang later appears when the pirate, Captain Hook sails to Neverland, along with Baelfire. They, led by Felix, search Hook's ship for Baelfire, believing that he has the heart of the truest believer. At first Hook lies about where he is but he then eventually hands Baelfire over. However, they were mistaken as Baelfire didn't fit the description of the child they were looking for. Afterwards, Baelfire was a Lost Boy for a while before he was taken back to Earth. Many years later, they and Felix greet Greg Mendell and Tamara and introduce themselves as the Home Office, the group that Greg and Tamara were working for to destroy magic. The two had just arrived in Neverland with Henry (who is Baelfire's son) as their hostage. Greg and Tamara were then shocked that the people they were working for were teenagers. Felix then told them that destroying magic was never their intention and demanded that they hand Henry over. When they refused, the Shadow killed Greg and the Lost Boys shot and wounded Tamara with a arrow, causing Henry to flee.
After Emma, Regina, Hook, David and Mary track down Peter Pan, the Lost Boys then ambushed and fought the group for a while. Peter Pan then called them off but not before they wounded David with a poison arrow. The Lost Boys were there when present when Henry briefly dueled with one of the boys. As Peter Pan was ready go to the skull rock with Henry, the Lost Boys were captured after knocked unconscious by Regina's spell. After Pan took Henry's heart, leaving Henry seemingly dead. They interrogated the boys asking where Pan was. At first, they refused to cooperate but they were eventually soothed by Emma, elaborate promised to take the boys with them back to Storybrooke and they eventually reveals Pan's location, which upsets Felix. After Pan's defeat, the boys went with the group back to Storybrooke and they made their new home there. After the curse is cast again, some of the Lost Boys, as well as many other Storybrooke citizens, gather at Neal's funeral to mourn his sudden death.
After a portal takes Hook and Black Beard to Neverland instead of Storybrooke, some of the boys stayed in Nederland and they argue over their dilemma until they hear the sound of drumming as well as whooping noises before they find themselves surrounded by a band of Lost Boys. One of the boys shouts for the others to kill the pirates, and as the group rush forward to attack them, Hook and Black Beard are forced to run for their lives. The two make it to the shoreline where there is a rowboat, but Black Beard escapes on it alone, while the Lost Boys continue pursuing Hook, who resumes running away to elude capture.
The Lost Boys, wanting revenge on Hook for Pan's death, eventually corner him. Hook attempts to bargain for his own life by offering them buried treasure and rum, but he is saved when the boys are taken out by Tiger Lily's arrows. At Pan's old camp, some of the Lost Boys are dancing around an open fire as others carry a roasted pig on a gurney. As they set the meal down, Tiger Lily fires an arrow at it, causing the Lost Boys to chase after her in retaliation, which gives Hook the time to grab some magic sap from a tree to free his own shadow. Before he can use the shadow to return to Emma, one of the Lost Boys notices him and alerts the others. When Hook tries to fly away, the Lost Boys grab his leg, with Hook eventually letting go of his shadow, whom he tells to get back to Emma and deliver the wand to her. The Lost Boys later prepare to execute Hook and Tiger Lily by burning them at the stake, but Emma bursts through a portal to save Hook. While Hook and Emma go back to Storybrooke, the Lost Boys continue looking for an escaped Tiger Lily, who flees into the forest without their notice.