Set Assistance to Helps Friends and Allies. In the AI Data tab, set the Aggression to Aggressive.Give the ID a name, set Child NPC as Player, and Relationship Level to Ally. Right-click in the Relationship tab to create a new relationship.Drag CurrentFollowerFaction, PotentialFollowerFaction and (optionally) PotentialMarriageFaction into the Faction tab.Set your companion's level and class in the Stats tab and adjust the Health, Magicka, and Stamina Offsets (usually 50).
Set either Essential or Protected, flag as Unique, and pick an authorized voice from the VoicesFollowerNeutral formlist. In the Traits tab, set the race and gender the same as your new character. This will export your character's appearance to your installation folder (the one up from Data that contains the Skyrim.exe). Exit the character creation screen and save your game.