I have a TM, by accident, & luckily I was lead here by a member who recognized her as such, both by looks & behaviors.
My biggest source of anxiety was learning how guardy TM's can become, & their independent thought, & the fact that if a threat is sensed, they WILL carry through & cannot be called off with commands.
So, that short history being said--I'm a big socializer to begin with, but I upped my game to every single day, some days multiple times per day.
Since he's so young, you've got an easier road ahead IMHO.
My advice would be keep doing what you are doing with the kids feeding him.
Not only does this help with food guarding, but it helps with soft mouth & being able to take things out of their mouth on a whim.
I have done this with every pup I've ever had, & it has worked with every dog, including Tessa.
Some dogs will become a little guardy over the food regardless, but it's positive affects with soft mouth still can't be overstated.
I assume you feed him at least 3x if not 4x per day at his age.
Make 1 or 2 of those meals a "not in the bowl meal".
Meaning get a zip lock baggie & put the food in it & go somewhere else with the pooch.
It can be another room, the yard, the park (once vaccinations are done)--and turn that meal into a multitasking training session.
Change up the kids, meaning not always the same person.
Feed the food one piece at a time, not all at once.
You can incorporate not only soft mouth, but sit, wait, down, stay etc into this session as time goes on-
It also instills a NILF type of thing.
-just do not have it be high activity like fetch or running/jumping type of stuff--it needs to be low activity-because of large breeds tendency towards bloat, they should not be highly active for about an hour after eating.
As far as socializing--get pooch out of his home environment & yard every single day (again once vaccinations are done).
Switch it up as much as possible, neighbors houses, park, trails, heavy traffic areas, loud places, stores, expose to dog savvy cats if you do not have any, expose to joggers, people on bikes/skateboards, playing kids etc.
As you incorporate the sit/stay thing with the hand fed meals, use the commands he is learning from then while you have him out as well.
One thing I am so thankful I taught Tessa from the beginning. I make her wait at the door, both on the inside, and once on the outside.
I have put her in a sit every single day, this is especially useful outside of the entry door. She will now wait for however long it takes if I am fumbling with keys, or getting the mail, or waiting for a dog or person to pass, meaning I am never dragged off the porch, she fully expects to wait. This will be a wonderful saving grace 50lbs from now