this may sound totally opposite of the above, and i would recommend it much more strongly if your son was a little older...and only you know your son and whether he is "responsible" enough to try this. but here's my take on it...your dog will respect the controller of the food...so if you can find a way to SAFELY have your son dole out the food to the pup, the pup should come to respect your son as alpha to himself. Again, only you know your son and if this would work. But if you can have your son put a small handful of food in the pup's bowl, let the pup eat, then look to your son to hand out the next handful that might do the trick. or piece by piece, or even just a scoop...and don't forget a healthy dose of praise for good behavior never hurts either
otherwise, i'd suggest using the leash method as your pup is a little on the young side to train the "sit stay" before any food will be handed out.
personally, i'll work with my dogs of all ages periodically to let me take their bowl away while they're eating, reach into their bowl and remove food or add tidbits while they're eating, etc just to make sure that they are not inclined toward any food guarding. Similarly, if they have a particularly captivating chew toy or a squeak they really love, i'll ask them to give it to me randomly. this reinforces my position as the "leader" and the one in charge of everything in my house, and since i will take the toy/treat and then give it right back, it also helps them to see that it's not a threat and they're not losing out on anything. this is also really handy if your dog ever gets hold of something they shouldn't have- my shepherd once got hold of a giant piece of cooked chicken at a bbq and could have been seriously injured by splintering bones had she not been trained this way. she surrendered the chicken immediately. my hope is that if someone other than me takes their toy away, that it will not result in any aggressive behavior. I also keep a very close eye out to make sure that my dogs are never teased- in my experience it's teasing a dog with something they want (playing "keep away"), that causes some pretty serious aggressive behaviors like snapping, grabbing etc. just something to keep in mind