I have three daughters, the youngest is 4.
I won't sugar coat it and say that it was a walk in the park from day one with a puppy and a four year old.
BUT, you know your child. If you think your son can understand some basic rules regarding interactions with the puppy, then it is absolutely doable.
I talked to my girls a lot before we got the puppy about how we act (no wrestling, no rough play, no tug, no taking toys or food from puppy, no picking puppy up, etc.) before we brought the puppy home. I printed a list of 10 Puppy Rules on a cute sign and put it up on the fridge.
The biggest issue is that golden puppies nip, bite and chew. On humans as well as things. And little kids have a tendancy to react to that in ways that just excite the puppy more....running away, climbing on furniture to get away from the nipping, screaming, trying to push the puppy away, etc. All of those things get the puppy more wound up. It's a vicious cycle. LOL!
I tought my kids to stick a toy in the dog's mouth and if that didn't work, to turn into a "tree" and not move. And as a last resort call a grown-up for help. Never push the puppy's face away, never run, jump or scream, etc. I still have to remind them. But it gets better all the time.
Also, we used baby gates and sliding doors to keep the puppy confined to the kitchen unless I could actively supervise. Puppies and kids both need their own space.
At this point, 6 months later, it's still a work in progress, but getting better every day as the puppy matures and my daughter continues to learn how to deal with him. This is them now (Katie will be 5 in March and Rocket is 8 months):
So, long story short.....you know your son, you know your own patience levels and how much time you have available. If you can put in the time to supervise and train both your son and the puppy, then go for it. He will have a friend for life!
ETA: Oh, and if you go with a puppy from a breeder, be up front with your breeders and tell them you are looking for a lower-energy pup that will be good with children. (Unless of course you want to do fieldwork or agility). When you go to visit breeders, take note of how the sire/dam behave....are they hyper and spastic, or calm and well-behaved? I wanted to take Rocket's mom home because she just kept planting her butt on my feet and resting her chin on my knee looking up at me for pets. Rocket does the same thing now. He's a total snuggler.