Shaun

Shaun is the son of the Sole Survivor in Fallout 4 and later known under the name of Father, the leader of The Institute, and also a potential antagonist, if choosing not to side with the Institute.

Background
From the appearance of Shaun, he was born around the summer of 2077. Just before the nuclear bombs hit The Commonwealth, he was taken into Vault 111, and put into a cryo chamber. He was kidnapped by two mysterious figures, one of them being Kelogg some 150 years later, from the arms of the spouse of the Sole Survivor. As Mama Murphy can explain to the Survivor, she can sense Shaun is still alive around 2287.

In 2227, The Institute discovered Vault 111, and with it the radiation-free survivors they needed to complete the synth project. He was abducted by its members and then raised by them as one of their own, later nicknamed "Father" for his role in providing the DNA required to complete the synths. In time, he became the acting director of the Institute. The Sole Survivor can find Shaun and may be forced to defeat him.

It is later revealed that he has a very aggressive form of cancer and one of the endings is to take his place as Director of The Institute after his death.

If The Survivor decides to eradicate The Institute and bring the young Synth with them they will receive a holodisk recorded by Father and given to them by the synth Shaun after being interacted with. The cybernetic Shaun tells The Sole Survivor "I didn't listen to it, so I dunno what it says, but I think it's important".

It is revealed that the young boy was reprogrammed to believe that the player character was their parent, as the first meeting between the synth and player character (who was led to believe that the synth was their missing son) caused the synth to become confused and call for help. The reason for him being reprogrammed is explained by the real Shaun in the holodisk, saying "I would ask only that you give him a chance. A chance to be a part of whatever future awaits the Commonwealth."

Appearances
Shaun appears only in Fallout 4.

Behind the scenes
In contrast, the Lone Wanderer, child of James from Fallout 3, was originally forced to slay their own father, but the part of the storyline was scrapped away.

Shaun (Fallout 4) Шон (Fallout 4) Shaun