Who doesn't want Liam Neeson as a dad? I mean, he'd go to crazy lengths to get you back! Although in Fallout 3, he's a lot less of the dad from Taken than a mild mannered scientist trying to make a difference.
James gives up his scientific pursuits to bring pure water to the wasteland to care for his son in Vault 101. Of course, the lure of science and progress pulls him out of the Vault and onto a new quest, with the Lone Wanderer following in his footsteps as the two go on adventures together across the wasteland.
In a stunning example of fatherly love, if you blow up Megaton and tell him about it, he totally forgives you. I'm honestly not sure if that's good or bad parenting. Later on in the game, James sacrifices himself so the Lone Wanderer can escape the Enclave soldiers.