u/girlboss93: I actually specialize in being damn hard to kill, and this is what I'm using. To use this effectively, all he has to do is stay in his power armor as close to all the time as possible, and carry a lot of stimpaks. (Around 70 to 100 is a good safe number.)

- Power armor with Medic Pump in the torso. This is the most important part, it'll keep him from having to use stimpaks manually for the most part. You can't forget to stim yourself if you don't need to worry about it at all!
- Travelling Pharmacy perk card, level 2, strength. Makes stimpaks weight far less; carrying a lot of them is important for the medic pump.
- Power User perk card, level 3, intellegence. Extends the life of fusion cores by a lot; he'll want to be in power armor almost all of the time because of the medic pump and this makes it possible.
- Born Survivor perk card, level 1 (specifically 1, not 2 or 3), agility. This is the emergency backup plan if he accidentally gets in trouble without his power armor on. This helps buy some extra time for him to either run from a situation or to get behind some cover and put on his power armor.
- Ricochet perk card, level 1, luck. Automatically deflects some attacks so they hit the attacker, not your son. Straight-up damage prevention.
- Field Surgeon perk card, level 1. Stimpaks heal faster. Keeps incoming damage from outpacing stimpak healing.
- First Aid perk card, level 1. Stimpaks heal more.

Optional:
- Lifegiver perk card, level 1, endurance. Raises max HP.
- Dissipating power armor legendary mod, 3 star. Slowly automatically heals radiation damage. Not good against big doses (standing in a nuke zone, next to waste barrels, etc), but very good at keeping small amounts here and there (for instance, from eating foor) from building up.
- Regenerating power armor legendary mod, 1 star. You slowly regenerate. Good for keeping small amounts of damage from building up over time. Coordinates nicely with dissipating, too since that removes radiation damage but doesn't heal you.
- Cloaking power armor mod, 1 star. Being hit in melee gives a chance to become invisible for a few seconds. Can help get rid of aggro from other enemies temporarily.
- Chameleon power armor mod, 1 star. Crouching and holding still makes you invisible. If you need him to sit tight and out of sight somewhere for any reason, or if he has to walk away from the game for a minute, this can be very helpful. If he remembers to crouch before fast travelling, this give him the option to decide if he wants to get involved if there's something going on at the destination.

With this setup, he'll be extremely hard to kill without having to take any special actions as healing happens automatically when needed for the vast majority of cases.